Molecular Biology International
Volume 2016 (2016), Article ID 9156735, 8 pages
http://dx.doi.org/10.1155/2016/9156735

Research Article

Analyses of Physcomitrella patens Ankyrin Repeat Proteins by Computational Approach

Niaz Mahmood¹ and Nahid Tamanna²

¹Graduate Program in Experimental Medicine, McGill University, Montreal, QC, Canada H2X 0A8
²Graduate Program in Biological Sciences, University of Manitoba, Winnipeg, MB, Canada R3T 2N2

Received 7 March 2016; Revised 18 May 2016; Accepted 25 May 2016

Academic Editor: Abdelali Hannoufa

Copyright © 2016 Niaz Mahmood and Nahid Tamanna. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

Ankyrin (ANK) repeat containing proteins are evolutionary conserved and have functions in crucial cellular processes like cell cycle regulation and signal transduction. In this study, through an entirely in silico approach using the first release of the moss genome annotation, we found that at least 54 ANK proteins are present in P. patens. Based on their differential domain composition, the identified ANK proteins were classified into nine subfamilies. Comparative analysis of the different subfamilies of ANK proteins revealed that P. patens contains almost all the known subgroups of ANK proteins found in the other angiosperm species except for the ones having the TPR domain. Phylogenetic analysis using full length protein sequences supported the subfamily classification where the members of the same subfamily almost always clustered together. Synonymous divergence (dS) and nonsynonymous divergence (dN) ratios showed positive selection for the ANK genes of P. patens which probably helped them to attain significant functional diversity during the course of evolution. Taken together, the data provided here can provide useful insights for future functional studies of the proteins from this superfamily as well as comparative studies of ANK proteins.

1. Introduction

Ankyrin (ANK) repeats, composed of around 30–34 amino acids, are evolutionary conserved protein domains found to be involved in mediating protein-protein interactions [1]. In metazoans, the ANK repeat containing proteins has diversified functions in important processes like signal transduction, cell-cycle regulation, maintaining the integrity of cytoskeleton, transcriptional regulation, inflammatory response, development, and different types of cellular transport mechanisms [2]. Defect in ANK proteins has been found in a number of human diseases. For example, the ankyrin repeat domain 11 (ANKRD11) proteins interact with and also enhance the transcriptional activity of p53. In breast cancer cell lines, the expression level of ANKRD11 decreases compared to controls [3]. Ankyrin dysfunction has been linked with fatal human arrhythmias, such as the “ankyrin-B syndrome” in which there is an aberration of the human ankyrin-B gene (ANK2) [4].

The importance of ANK repeats can be underlined by their abundance in virtually all phyla. In photosynthetic organisms, these proteins have also been shown to be involved in a number of important physiological processes. Zhang and colleagues first reported on a light-dependent plant ANK protein which is involved in cell differentiation and development in Arabidopsis [5]. EMB506, a five-ANK repeat containing protein, has been shown to be essential for embryogenesis in Arabidopsis [6]. Another ANK protein, known as BOP1, is required for leaf morphogenesis [7]. XBAT32 and XBAT35 are linked with the regulation of ethylene biosynthesis [8, 9] and ethylene signaling [10], respectively. Several ANK proteins have been demonstrated to play role in responses to biotic and abiotic stresses in plants. The expression of rice OsBIANK1 gene, encoding proteins containing ANK repeats, is altered in pathogen infected rice-seedlings compared to that of the controls which suggests its involvement in disease resistance response [11]. Furthermore, Yan and colleagues have shown that the Arabidopsis ANK protein, AKR2, might be involved in regulating antioxidant metabolism during disease resistance and stress responses [12].

The recent advancement in genome sequencing has enabled the genome-wide identification and characterization of ANK proteins from several photosynthetic species like Arabidopsis [14], rice [15], and tomato [16]. The availability of the genome sequence of Physcomitrella patens [17] provided us with an excellent opportunity for a genome-wide analysis of this ANK family in bryophyte. Here, we report analyses of the ANK proteins of P. patens using first release of the moss genome annotation.

2. Methods

2.1. Data Retrieval and Identification of ANK Proteins

The publicly available protein sequences of P. patens were downloaded from the JGI Phytozome database (first release of the moss genome annotation) [18] and domain annotation of these proteins was done by InterProScan [19]. Then ANK proteins were screened by searching for the PF00023 domain using an in-house Perl script as described in a previous paper [20]. BLASTP was carried out with NCBI nonredundant protein database using the sequences retrieved from InterProScan as queries. After that, the candidate sequences were curated manually using available annotations in GenBank and existing literature. The molecular weights and isoelectric points were determined separately from online web server (http://www.bioinformatics.org/sms2/). Subcellular localization was predicted by the online web server of ProtComp 9.0 (http://www.softberry.com/berry.phtml?topic=protcomppl&group=help&subgroup=proloc).

2.2. Classification and Phylogenetic Analyses of the ANK Proteins

The proteins were classified into different subgroups based on the presence of additional conserved domains other than the ANK domain as described previously [15, 21]. Phylogenetic tree file was constructed by the online webserver, SATCHMO-JS [22]; and the tree was visualized by the Molecular Evolutionary Genetics Analysis (MEGA) software version 4.1 [23]. In addition, synonymous and nonsynonymous substitution pattern were determined as described previously [24].

3. Results and Discussion

Using our approach, we were able to identify a total of 54 proteins having at least one ANK repeat in P. patens (in the first released annotation of the moss genome). The identified sequences were further verified in a reiterative process through manual curation. The percentage of ANK proteins in P. patens (0.15%) is a bit lower compared to the other species from the tracheophyte lineage as listed in Figure 1(a).

(a)

(b)

(c)

(d)

Figure 1: (a) The total number of predicted ANK proteins identified by different groups in the four sequenced angiosperm genomes (Oryza sativa, Zea mays, Arabidopsis thaliana, and Solanum lycopersicum) along with their bryophyte counterpart P. patens. The total number of predicted proteins of each species is also provided. See source column for references. (b) Distribution of PpANK proteins according to their length. (c) Number of putative ANK repeats per protein shown graphically by bar diagram. The horizontal axis in the figure represents different numbers of ANK repeats while the vertical axis represents the frequency of the proteins corresponding to different number of repeats. A large percentage (41%) of the PpANKs have 3 repeats within their sequence, as seen in the graph. (d) The consensus sequence of the P. patens ankyrin repeat motif.

The identified sequences from P. patens were designated as PpANK1, PpANK2,…,PpANK54, respectively, for analysis purpose during this study (Table 1). Figure 1(b) shows the distribution of the PpANKs according to the number of amino acids they contain within their primary sequence. The largest protein (PpANK8) had a length of 1,088 amino acids, while the shortest one (PpANK48) contained only 74 amino acids. The molecular weights (MW) and isoelectric points (PI) of the PpANK proteins deduced from their protein sequences are listed in Table 1. In addition, it was observed that these 54 PpANK proteins contained a total of 163 ANK repeats among themselves. The number of ANK repeats per protein in P. patens ranged in between 1 and 9, whereas the average number of repeats per protein was 3. The frequency of the proteins having different number of ANK repeats is shown in Figure 1(c). The highest number of repeats (9) was found in PpANK43 whereas PpANK4, PpANK18, PpANK22, PpANK33, and PpANK49 had just one ANK repeat motif each. In general, most ANK proteins have two to six repeats; and the largest known number of repeats is 34 that was found in a Giardia lamblia protein [25].

Table 1: List of ANK proteins identified in P. patens.

NCBI accession number
Our nomenclature
# of repeats
Length (A.A.s)
MW (KD)
PI

XP_001770032
PpANK1
3
176
18.54
4.02

XP_001770249
PpANK2
4
211
22.88
9.52

XP_001771297
PpANK3
2
425
47.57
8.63

XP_001774650
PpANK4
1
418
47.15
7.01

XP_001775781
PpANK5
4
364
40.21
8.24

XP_001756372
PpANK6
3
144
15.3
4.43

XP_001756378
PpANK7
3
376
41.11
4.48

XP_001777467
PpANK8
2
1088
116.86
8.18

XP_001779325
PpANK9
5
425
45.81
6.71

XP_001757508
PpANK10
2
463
50.67
7.19

XP_001782286
PpANK11
3
350
38.41
4.15

XP_001782585
PpANK12
3
121
12.8
6.29

XP_001759240
PpANK13
2
440
48.17
6.19

XP_001783731
PpANK14
3
421
47.49
7.01

XP_001784155
PpANK15
3
442
49.87
7.19

XP_001765240
PpANK16
3
419
47.13
7.75

XP_001765521
PpANK17
3
167
18.4
8.75

XP_001753203
PpANK18
1
82
8.73
4.67

XP_001766044
PpANK19
3
342
37.48
4.19

XP_001767452
PpANK20
2
412
46.92
8.12

XP_001771908
PpANK21
2
438
48.19
8.08

XP_001755743
PpANK22
1
291
31.45
8.6

XP_001784959
PpANK23
6
247
27.98
6.27

XP_001762570
PpANK24
5
437
47.16
7.64

XP_001764006
PpANK25
2
337
37.55
4.44

XP_001753287
PpANK26
3
343
36.03
4.09

XP_001774971
PpANK27
3
378
41.73
5.74

XP_001779754
PpANK28
4
234
25.26
8.85

XP_001759321
PpANK29
3
608
68.4
6.69

XP_001760427
PpANK30
2
377
41.77
6.23

XP_001765151
PpANK31
4
625
69.45
5.03

XP_001765275
PpANK32
4
351
37.69
6.85

XP_001767776
PpANK33
1
752
82.78
9.39

XP_001771059
PpANK34
4
451
48.45
5.64

XP_001780358
PpANK35
3
634
71.25
8.42

XP_001763413
PpANK36
4
473
50.65
5.08

XP_001773791
PpANK37
3
271
30.45
4.58

XP_001773863
PpANK38
2
107
11.37
3.88

XP_001774458
PpANK39
2
731
82.73
7.11

XP_001779036
PpANK40
2
721
82.01
7.12

XP_001759158
PpANK41
2
752
84.75
8.64

XP_001784362
PpANK42
3
414
47.27
6.51

XP_001765211
PpANK43
9
795
90.39
7.16

XP_001770763
PpANK44
6
1060
114.9
8.03

XP_001765353
PpANK45
3
612
67.04
8.35

XP_001754260
PpANK46
5
402
43.17
7.72

XP_001771412
PpANK47
3
285
32.42
4.04

XP_001755344
PpANK48
2
74
7.65
4.34

XP_001775223
PpANK49
1
910
101.79
7.62

XP_001758257
PpANK50
3
380
42.3
8.66

XP_001758416
PpANK51
3
86
9.13
7.16

XP_001782553
PpANK52
3
111
11.72
6.67

XP_001784176
PpANK53
2
367
40.47
7.52

XP_001760375
PpANK54
3
130
14.03
10.41

The consensus ankyrin repeat sequence in P. patens, [ND]AxDKDGRT[PA]LHLAAxxGHxE[VA]-V[EK]LLLD[AH]GA[DN][VP], was generated by MEME webserver (http://meme.sdsc.edu/meme/intro.html) and visualized by Weblogo [26] as shown in Figure 2(a). The consensus ANK sequence in P. patens had a length of 33 amino acids and was conserved at the residues that are needed to retain the stacked L-shaped structure for protein-protein interaction, as mentioned by Mosavi and colleagues [27].

(a) 

(b)

(c)

(d)

Figure 2: (a) Number of ANK proteins in each subfamily in P. patens, rice, maize, Arabidopsis, and tomato denoted as Pp, Os, Zm, At, and Sl, respectively. (b) Schematic representation of the structure of representative PpANK proteins from each subfamily. The figures shown here are not drawn to scale. (c) Evolutionary tree constructed from the full-length protein sequences of PpANK proteins. Different colors correspond to different subfamilies which are described in the right side of the tree. In most cases, the members of the same subfamily were clustered together. (d) Synonymous divergence (dS) and nonsynonymous divergence (dN) ratios of the ANK genes in P. patens.

Based on their domain compositions, the predicted PpANK proteins were classified into nine subfamilies (Figure 2(a)). We have observed that a significant number of the PpANK proteins (21) had no other recognizable domain apart from the conserved ankyrin repeat and were classified as ANK-M. Proteins containing other known functional domains apart from the ANK domains were classified into the following subfamilies. Six proteins containing the RING finger domains were grouped as ANK-RF; three proteins containing the zinc-finger domain were designated as ANK-ZnF. BAR, PH and ArfGap domain containing proteins were grouped as ANK-BPA (3 members). The ANK-BTB subfamily (3 members) had broad-complex, tramtrack, and bric-a-brac domains. Nine of the PpANK proteins having either serine/threonine or tyrosine kinase domain were classified as ANK-PK. Three proteins having the Acetyl-CoA binding domain were classified as ACBP. Two proteins having the GPCR-chapero-1 domain were classified as ANK-GPCR. This specific subfamily containing the GPCR domain has only been reported to be found in tomato and has not been reported in model plant species like Arabidopsis and rice [16] (Figure 2(a)). The rest of the PpANK proteins that contained other domains including CHROMO, IQ, TM, and RCC1 were grouped as ANK-O. The structure of representative proteins from each subfamily is shown in Figure 2(b). There were no ANK proteins having the TPR domains (ANK-TPR) in P. patens, even though ANK proteins having these two domains are present in both Arabidopsis and rice [14, 15].

Next, we constructed a phylogenetic tree to compare between the members of different subfamilies of PpANKs. The tree file was generated from the Hidden Markov Model (HMM) based multiple sequence alignments of the sequences done by SATCHMO-JS and visualized by the Molecular Evolutionary Genetics Analysis (MEGA) software version 4.1 [23]. Interestingly, in most of the cases, members of the same subfamily were clustered together in the phylogenetic tree (Figure 2(c)).

We also analyzed the synonymous and nonsynonymous substitution patterns of the coding sequences of the genes encoding the ANK proteins in P. patens. The corresponding nucleotide sequences of the PpANK proteins were obtained from NCBI. Then we aligned the sequences using MEGA 4.1 and obtained the synonymous divergence (dS) and nonsynonymous divergence (dN) ratios. The ratio suggested positive selection for the genes of ANK superfamily of P. patens (Figure 2(d)). The codon based Z test indicated positive selection (data not shown) for most of the pairwise comparisons of the ANK genes. This further explains the fact that the ANK repeat encoding genes have acquired significant functional diversity by extensive domain shuffling or emerged multiple times independently, as a result of convergent evolution or parallel evolution or both [21].

In order to elucidate the function of a protein within a living cell, predicting the location where it resides in the cell is essential. In this study we have used ProtComp version 9.0 for predicting the subcellular localization of the PpANK proteins. The output revealed that the proteins are dispersed throughout the cells (Figure 3(a)). A large percentage (33%) of the PpANKs are located in the nucleus. Detailed information on the localization of each protein can be found in Supplementary Table  1 in Supplementary Material available online at http://dx.doi.org/10.1155/2016/9156735. We also tried to analyze if there is any relationship between the subfamilies of PpANKs with their respective subcellular localization. Interestingly, we have found that all the members of the ANK-BPA subfamily had similar localization pattern, that is, in the extracellular region (Additional File 1, Supplementary Table  1). For all the other subfamilies, we did not see any distinct pattern in their localization.

(a)

(b)

Figure 3: (a) Percentage distribution of PpANKs in different locations of the cells as predicted by ProtComp version 9.0. (b) Distribution of molecular function of the PpANK proteins as obtained from Blast2Go [13].

The PpANK sequences were also compared with the proteins in of NCBI nonredundant protein database which showed their homology with ANK proteins from diverse species ranging from bacteria to green algae to plants (Additional File 1, Supplementary Table  2). Not surprisingly, in many of the cases, the proteins having significant similarity with the corresponding PpANKs have functions either as protein binders or as kinases (Figure 3(b)). This further clarifies the fact that ANK proteins play significant role in protein-protein interaction and cellular signaling pathways.

4. Conclusion

This study mainly focused on the sequences ANK proteins: their classification and phylogenetic analysis by using the first release of the moss genome annotation. We are aware that newer versions of the moss genome annotation are already available in Phytozome. As such the results shown here do not provide a complete overview of the whole repertoire of P. patens ankyrin proteins. Moreover, experimental verification and wet-lab functional studies of the genes encoding these proteins are necessary to come to any definite conclusion about their biological function. Nevertheless this may serve as a useful reference for more detailed functional analyses as well as for the selection of appropriate candidate genes for further studies and genetic manipulation of P. patens ankyrin proteins.

Competing Interests

The authors declare that they have no competing interests.

Authors’ Contributions

Niaz Mahmood conceptualized the study. Both Niaz Mahmood and Nahid Tamanna analyzed and interpreted the data; and Niaz Mahmood wrote the paper. The final version of the paper is approved by both of the authors.

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