title: Identification and characterization of two mature isoforms of retinoschisin in murine retina.
abstract: Retinoschisin (RS) is a 24 kDa secreted protein expressed in retina and is required for the structural and functional integrity of the retina. RS has been predicted to serve as an adhesive protein but the precise molecular mechanism by which it functions in retina is not yet known. During investigations on structural and functional aspects of RS in murine retina using proteomic tools, we identified two isoforms of RS that differed in mass by 200 Da with no apparent change in charge. Mass spectra and amino acid sequence analysis of the tryptic peptides revealed that these isoforms differed by two amino acids at the N-terminus which suggested processing of RS signal sequence at two cleavage sites by signal peptidase as the basic mechanism underlying the occurrence of two mature RS isoforms in retina. Bioinformatic analysis identified two potential cleavage sites (between amino acids 21-22 and 23-24) in RS signal sequence. The flexibility of the signal peptidase to cleave at two sites is correlated to the amino acid composition of the RS signal sequence. This finding represents a rare example of a naturally occurring signal sequence cleavage at more than one site in vivo.
authors.affiliation: Section for Translational Research in Retinal and Macular Degeneration, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Camasamudram
authors.initials: C
authors.lastname: Vijayasarathy
authors.forename: Mary Ann
authors.initials: MA
authors.lastname: Gawinowicz
authors.forename: Yong
authors.initials: Y
authors.lastname: Zeng
authors.forename: Yuichiro
authors.initials: Y
authors.lastname: Takada
authors.forename: Ronald A
authors.initials: RA
authors.lastname: Bush
authors.forename: Paul A
authors.initials: PA
authors.lastname: Sieving
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D015815:Cell Adhesion Molecules / Q000737:chemistry* / Q000378:metabolism; D005136:Eye Proteins / Q000737:chemistry* / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry; D020033:Protein Isoforms; D011499:Protein Processing, Post-Translational; D017434:Protein Structure, Tertiary; D040901:Proteomics / Q000379:methods; D012160:Retina / Q000378:metabolism*; D041441:Retinoschisis / Q000378:metabolism; D014357:Trypsin / Q000737:chemistry
chemical_list: D015815:Cell Adhesion Molecules; D005136:Eye Proteins; D010455:Peptides; D020033:Protein Isoforms; C491843:RS1 protein, mouse; D014357:Trypsin