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Fluorescence investigations on choline phospholipid binding and chemical unfolding of HSP-1/2, a major protein of horse seminal plasma

Paper ID Volume ID Publish Year Pages File Format Full-Text
29884 44445 2016 10 PDF Available
Title
Fluorescence investigations on choline phospholipid binding and chemical unfolding of HSP-1/2, a major protein of horse seminal plasma
Abstract

•Microenvironment of Trp residues in HSP-1/2 was investigated by fluorescence methods.•Binding of choline containing ligand shields Trp residues of HSP-1/2 from quenching.•Chaotrope-induced unfolding of native HSP-1/2 was partial with low cooperativity.•Complete cooperative unfolding was observed upon reduction of disulfide bonds.•Ligand binding and polydispersity modulate chaotrope-induced unfolding of HSP-1/2.

Seminal fibronectin type-II (Fn-II) proteins interact with choline phospholipids present on the sperm plasma membrane and play a crucial role in sperm capacitation. Crystal structure of phosphorylcholine (PrC) complex of PDC-109, the major bovine Fn-II protein, together with fluorescence spectroscopic studies has shown that tryptophan residues are crucial for its specific interaction with choline phospholipids. In the present study, the heterogeneity and microenvironment of tryptophan residues in HSP-1/2, a major protein of horse seminal plasma (which is homologous to PDC-109) were investigated in the native state, in the presence of PrC and phosphatidylcholines (PCs) with short (valeryl, C-5) and long (myristoyl, C-14) chains, and upon denaturation using fluorescence quenching, time-resolved fluorescence and red-edge excitation shift (REES) measurements. The results obtained show that the environment of tryptophan residues in HSP-1/2 is more heterogeneous as compared to that in PDC-109. Binding of choline containing ligands afforded a protection to the tryptophan residues with the shielding order being: PrC ≤ divalaroyl PC < dimyristoyl PC. REES value obtained for HSP-1/2 (3.5 nm) is smaller than that of observed for PDC-109 (4 nm) and binding to PrC and DVPC reduced the REES to 1 nm. HSP-1/2 exhibits only partial unfolding with chemical denaturants with no cooperativity, whereas complete unfolding was observed in the presence of 10 mM dithiothreitol, indicating that disulfide linkages prevent complete unfolding of the protein. In the presence of PrC the transition midpoints shifted to higher concentrations of the denaturant together with a broadening of the sigmoidal transitions, indicating that ligand binding as well as polydispersity modulate the unfolding process.

Keywords
DVPC, divalaroylphosphatidylcholine; DMPC, dimyristoylphosphatidylcholine; DTT, dithiothreitol; Fn-II, fibronectin type II; Gdm.Cl, guanidinium hydrochloride; Gdm.SCN, guanidinium thiocyanate; HSP-1/2, horse seminal plasma protein-1/2; Lyso-PC, lyso-phosp
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Fluorescence investigations on choline phospholipid binding and chemical unfolding of HSP-1/2, a major protein of horse seminal plasma
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Publisher
Database: Elsevier - ScienceDirect
Journal: Journal of Photochemistry and Photobiology B: Biology - Volume 158, May 2016, Pages 89–98
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Bioengineering
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us