Somatomedin B

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Somatomedin B domain

Somatomedin B is a serum factor of unknown function, is a small cysteine-rich peptide, derived proteolytically from the N-terminus of the cell-substrate adhesion protein vitronectin.[1] Cys-rich somatomedin B-like domains are found in a number of proteins,[2] including plasma-cell membrane glycoprotein (which has nucleotide pyrophosphate and alkaline phosphodiesterase I activities)[3] and placental protein 11 (which appears to possess amidolytic activity).

The SMB domain of vitronectin has been demonstrated to interact with both the urokinase receptor and the plasminogen activator inhibitor-1 (PAI-1) and the conserved cysteines of the NPP1 somatomedin B-like domain have been shown to mediate homodimerization.[4] As shown in the following schematic representation below the SMB domain contains eight Cys residues, arranged into four disulfide bonds. It has been suggested[by whom?] that the active SMB domain may be permitted considerable disulfide bond heterogeneity or variability, provided that the Cys25-Cys31 disulfide bond is preserved. The three-dimensional structure of the SMB domain is extremely compact and the disulfide bonds are packed in the centre of the domain forming a covalently bonded core.[5] The structure of the SMB domain presents a new protein fold, with the only ordered secondary structure being a single-turn alpha-helix and a single-turn 3(10)-helix.[6]


'C': conserved cysteine probably involved in a disulfide bond. '*': position of the pattern.

Human proteins containing this domain[edit]



  1. ^ Jenne D, Stanley KK (1987). "Nucleotide sequence and organization of the human S-protein gene: repeating peptide motifs in the "pexin" family and a model for their evolution". Biochemistry. 26 (21): 6735–6742. doi:10.1021/bi00395a024. PMID 2447940.
  2. ^ Jenne D (1991). "Homology of placental protein 11 and pea seed albumin 2 with vitronectin". Biochem. Biophys. Res. Commun. 176 (3): 1000–1006. doi:10.1016/0006-291X(91)90381-G. PMID 1710108.
  3. ^ Rebbe NF, Tong BD, Finley EM, Hickman S (1991). "Identification of nucleotide pyrophosphatase/alkaline phosphodiesterase I activity associated with the mouse plasma cell differentiation antigen PC-1". Proc. Natl. Acad. Sci. U.S.A. 88 (12): 5192–5196. doi:10.1073/pnas.88.12.5192. PMC 51838. PMID 1647027.
  4. ^ Gijsbers R, Ceulemans H, Bollen M (2003). "Functional characterization of the non-catalytic ectodomains of the nucleotide pyrophosphatase/phosphodiesterase NPP1". Biochem. J. 371 (Pt 2): 321–330. doi:10.1042/BJ20021943. PMC 1223305. PMID 12533192.
  5. ^ Dyson HJ, Kamikubo Y, Kroon G, Curriden S, Neels JG, Churchill MJ, Dawson P, Jagielska A, Scheraga HA, Loskutoff DJ, De Guzman R, OBdziej S (2004). "Disulfide bonding arrangements in active forms of the somatomedin B domain of human vitronectin". Biochemistry. 43 (21): 6519–6534. doi:10.1021/bi049647c. PMID 15157085.
  6. ^ Carrell RW, Zhou A, Read RJ, Huntington JA, Pannu NS (2003). "How vitronectin binds PAI-1 to modulate fibrinolysis and cell migration". Nat. Struct. Biol. 10 (7): 541–544. doi:10.1038/nsb943. PMID 12808446.
This article incorporates text from the public domain Pfam and InterPro: IPR001212