title: Conserved C-terminal nascent peptide binding domain of HYPK facilitates its chaperone-like activity.
abstract: Human HYPK (Huntingtin Yeast-two-hybrid Protein K) is an intrinsically unstructured chaperone-like protein with no sequence homology to known chaperones. HYPK is also known to be a part of ribosome-associated protein complex and present in polysomes. The objective of the present study was to investigate the evolutionary influence on HYPK primary structure and its impact on the protein's function. Amino acid sequence analysis revealed 105 orthologs of human HYPK from plants, lower invertebrates to mammals. C-terminal part of HYPK was found to be particularly conserved and to contain nascent polypeptide-associated alpha subunit (NPAA) domain. This region experiences highest selection pressure, signifying its importance in the structural and functional evolution. NPAA domain of human HYPK has unique amino acid composition preferring glutamic acid and happens to be more stable from a conformational point of view having higher content of a-helices than the rest. Cell biology studies indicate that overexpressed C-terminal human HYPK can interact with nascent proteins, co-localizes with huntingtin, increases cell viability and decreases caspase activities in Huntington's disease (HD) cell culture model. This domain is found to be required for the chaperone-like activity of HYPK in vivo. Our study suggested that by virtue of its flexibility and nascent peptide binding activity, HYPK may play an important role in assisting protein (re)folding.
authors.affiliation: Crystallography and Molecular Biology Division, Saha Institute of Nuclear Physics, Kolkata 700 064, India, rcswasti@ccmb.res.in.
authors.forename: Swasti
authors.initials: S
authors.lastname: Raychaudhuri
authors.forename: Rachana
authors.initials: R
authors.lastname: Banerjee
authors.forename: Subhasish
authors.initials: S
authors.lastname: Mukhopadhyay
authors.forename: Nitai P
authors.initials: NP
authors.lastname: Bhattacharyya
mesh_terms: D000595:Amino Acid Sequence; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism*; D016000:Cluster Analysis; D017124:Conserved Sequence / Q000235:genetics; D017931:DNA Primers / Q000235:genetics; D006801:Humans; D018613:Microscopy, Confocal; D008957:Models, Genetic; D018832:Molecular Chaperones / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D010802:Phylogeny; D011487:Protein Conformation; D017434:Protein Structure, Tertiary / Q000235:genetics; D020539:Sequence Analysis, Protein; D017385:Sequence Homology; D013778:Tetrazolium Salts; D013844:Thiazoles
chemical_list: D002352:Carrier Proteins; D017931:DNA Primers; C526912:HYPK protein, human; D018832:Molecular Chaperones; D013778:Tetrazolium Salts; D013844:Thiazoles; C096099:nascent-polypeptide-associated complex; C022616:thiazolyl blue