Zahedi K
Division of Nephrology, Children's Hospital Research Foundation, University of Cincinnati College of Medicine, Cincinnati, Ohio 45229-3039, USA.
J Biol Chem. 1996 Jun 21;271(25):14897-902. doi: 10.1074/jbc.271.25.14897.
Serum amyloid P (SAP), a member of the evolutionarily conserved pentraxin family, is a normal component of a number of basement membranes, including glomerular and alveolar. In vitro SAP binds to a variety of proteins including fibronectin, proteoglycans, and the collagen-like region of the complement component C1q. In these studies, binding of SAP to type IV collagen, a major component of basement membrane, was examined. Purified SAP binds to human and mouse type IV collagen but not type I, II, or III collagens. Binding of SAP to type IV collagen is dependent on the presence of Ca2+. This binding is saturable with a Kd approximately 1.2 x 10(-7) M based on solid phase binding and 4 x 10(-8) M based on the IC50 value from fluid phase binding data. Binding of SAP to type IV collagen was inhibited by both SAP and C-reactive protein (CRP). However, a 5-fold molar excess of CRP as compared with SAP was required to inhibit the SAP binding by 50%. Binding of SAP to type IV collagen was inhibited by both collagen IV and C1q but not by phosphatidylethanolamine or bovine serum albumin. The inhibition data indicate that SAP may bind to the triple helical region of type IV collagen via a site distinct from its galactan binding site. The most likely site of SAP involved in its interaction with type IV collagen may be the region spanning amino acid residues 108-120, which shows a great deal of sequence homology (60% strict identity) with the CRP region implicated in its binding to the collagen-like region of the C1q molecule.
血清淀粉样蛋白P（SAP）是进化上保守的五聚体蛋白家族的成员，是包括肾小球和肺泡在内的许多基底膜的正常组成部分。在体外，SAP可与多种蛋白质结合，包括纤连蛋白、蛋白聚糖和补体成分C1q的胶原样区域。在这些研究中，检测了SAP与基底膜主要成分IV型胶原的结合。纯化的SAP可与人及小鼠的IV型胶原结合，但不与I、II或III型胶原结合。SAP与IV型胶原的结合依赖于Ca2+的存在。基于固相结合，这种结合具有饱和性，Kd约为1.2×10（-7）M；基于液相结合数据的IC50值，Kd约为4×10（-8）M。SAP和C反应蛋白（CRP）均可抑制SAP与IV型胶原的结合。然而，与SAP相比，需要5倍摩尔过量的CRP才能抑制50%的SAP结合。IV型胶原和C1q均可抑制SAP与IV型胶原的结合，但磷脂酰乙醇胺或牛血清白蛋白则无此作用。抑制数据表明，SAP可能通过一个与其半乳聚糖结合位点不同的位点与IV型胶原的三螺旋区域结合。参与SAP与IV型胶原相互作用的最可能位点可能是跨越氨基酸残基108 - 120的区域，该区域与CRP中涉及其与C1q分子胶原样区域结合的区域具有大量的序列同源性（60%严格同一性）。
