The SAAS granin exhibits structural and functional homology to 7B2 and contains a highly potent hexapeptide inhibitor of PC1.
Prohormone convertases (PCs) 1 and 2 are thought to mediate the proteolytic cleavage of many peptide precursors. Endogenous inhibitors of both PC1 and PC2 have now been identified; the 7B2 protein is a nanomolar inhibitor of PC2, while the novel protein proSAAS was recently reported to be a micromolar inhibitor of PC1 [Fricker et al. (2000) J. Neurosci. 20, 639-648]. We here report evidence that 7B2 and proSAAS exhibit several elements of structural and functional homology. Firstly, 26 kDa human, mouse and rat proSAAS, like all vertebrate 7B2s, contain a proline-rich sequence within the first half of the molecule and also contain a C-terminal 40 residue peptide (SAAS CT peptide) separated from the remainder of the protein by a furin consensus sequence. The SAAS CT peptide contains the precise sequence of a hexapeptide previously identified by combinatorial peptide library screening as a potent inhibitor of PC1, and the vast majority of the inhibitory potency of proSAAS can be attributed to this hexapeptide. Further, like the 7B2 CT peptide, SAAS CT-derived peptides represent tight-binding competitive convertase inhibitors with nanomolar potencies. Lastly, recombinant PC1 is able to cleave the proSAAS CT peptide to a product with a mass consistent with cleavage following the inhibitory hexapeptide. Taken together, our results indicate that proSAAS and 7B2 may comprise two members of a functionally homologous family of convertase inhibitor proteins.
Cameron
A
A
Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center, 1901 Perdido St., New Orleans, LA, USA.
Fortenberry
Y
Y
Lindberg
I
I
D000595:Amino Acid Sequence; D000818:Animals; D016282:Aspartic Acid Endopeptidases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D001667:Binding, Competitive; D016466:CHO Cells; D006224:Cricetinae; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D045683:Furin; D007700:Kinetics; D051379:Mice; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000378:metabolism*; D051859:Neuroendocrine Secretory Protein 7B2; D009479:Neuropeptides / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D010446:Peptide Fragments / Q000378:metabolism / Q000494:pharmacology; D010907:Pituitary Hormones / Q000737:chemistry / Q000378:metabolism*; D045664:Proprotein Convertase 1; D045706:Proprotein Convertase 2; D043484:Proprotein Convertases; D011485:Protein Binding; D011498:Protein Precursors / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D013381:Subtilisins / Q000037:antagonists & inhibitors / Q000378:metabolism
D004791:Enzyme Inhibitors; D009419:Nerve Tissue Proteins; D051859:Neuroendocrine Secretory Protein 7B2; D009479:Neuropeptides; C403532:PCSK1N protein, human; D010446:Peptide Fragments; D010907:Pituitary Hormones; D011498:Protein Precursors; D011994:Recombinant Proteins; D043484:Proprotein Convertases; D013381:Subtilisins; D045683:Furin; C473656:Pcsk1 protein, mouse; D045664:Proprotein Convertase 1; D045706:Proprotein Convertase 2; D016282:Aspartic Acid Endopeptidases