title: Structural and binding studies of SAP-1 protein with heparin.
abstract: SAP-1 is a low molecular weight cysteine protease inhibitor (CPI) which belongs to type-2 cystatins family. SAP-1 protein purified from human seminal plasma (HuSP) has been shown to inhibit cysteine and serine proteases and exhibit interesting biological properties, including high temperature and pH stability. Heparin is a naturally occurring glycosaminoglycan (with varied chain length) which interacts with a number of proteins and regulates multiple steps in different biological processes. As an anticoagulant, heparin enhances inhibition of thrombin by the serpin antithrombin III. Therefore, we have employed surface plasmon resonance (SPR) to improve our understanding of the binding interaction between heparin and SAP-1 (protease inhibitor). SPR data suggest that SAP-1 binds to heparin with a significant affinity (KD = 158 nm). SPR solution competition studies using heparin oligosaccharides showed that the binding of SAP-1 to heparin is dependent on chain length. Large oligosaccharides show strong binding affinity for SAP-1. Further to get insight into the structural aspect of interactions between SAP-1 and heparin, we used modelled structure of the SAP-1 and docked with heparin and heparin-derived polysaccharides. The results suggest that a positively charged residue lysine plays important role in these interactions. Such information should improve our understanding of how heparin, present in the reproductive tract, regulates cystatins activity.
authors.affiliation: Department of Biophysics, All India Institute of Medical Sciences, New Delhi, 110029, India.
authors.forename: Vikash K
authors.initials: VK
authors.lastname: Yadav
authors.forename: Rahul S
authors.initials: RS
authors.lastname: Mandal
authors.forename: Bhanwar L
authors.initials: BL
authors.lastname: Puniya
authors.forename: Rahul
authors.initials: R
authors.lastname: Kumar
authors.forename: Sharmistha
authors.initials: S
authors.lastname: Dey
authors.forename: Sarman
authors.initials: S
authors.lastname: Singh
authors.forename: Savita
authors.initials: S
authors.lastname: Yadav
mesh_terms: D001665:Binding Sites; D006493:Heparin / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D062105:Molecular Docking Simulation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012697:Serine Endopeptidases / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D020349:Surface Plasmon Resonance
chemical_list: D006493:Heparin; D012697:Serine Endopeptidases
keywords: binding affinity; cystatins; heparin; key residues; molecular docking; surface plasmon resonance