Abstract
Eicosapenta peptide repeats (EPRs) occur exclusively in flowering plant genomes and exhibit very high amino acid residue conservation across occurrence. DNA and amino acid sequence searches yielded no indications about the function due to absence of similarity to known sequences. Tertiary structure of an EPR protein coded by rice (Oryza sativa japonica) cDNA (GI: 32984786) was determined based on ab initio methodology in order to draw clues on functional significance of EPRs. The resultant structure comprised of seven α-helices and thirteen anti-parallel β-sheets. Surface-mapping of conserved residues onto the structure deduced that (i) regions equivalent to β α4- the primary function of EPR protein could be Ca2+ binding, and (iii) the putative EPR Ca2+ binding domain is structurally similar to calcium-binding domains of plant lectins. Additionally, the phylogenetic analysis showed an evolving taxa-specific distribution of EPR proteins observed in some GNA-like lectins.
Highlights
Repeat proteins form an abundant and ubiquitous class of proteins
Computational screening of rice full-length cDNA sequences discovered the existence of proteins containing eicosapenta peptide repeats (EPRs) a novel class of repeat proteins [2]
EPRs occur in multiple copies, they are far fewer compared to PPRs
Summary
Repeat proteins form an abundant and ubiquitous class of proteins. These proteins are characterized by tandem homologous structural motifs of 20-40 amino acids and are categorized based on their structures. EPRs are unique by specific occurrence only in flowering plants and highly conserved amino acid sequences. Protein function can be annotated, based on different protein features such as 3D fold, sequence, structural motifs and functional sites using likelihoods [4].
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