Thermodynamics of phosphorylcholine and lysophosphatidylcholine binding to the major protein of bovine seminal plasma, PDC-109.
PDC-109 binds to sperm plasma membranes by specific interaction with choline phospholipids and induces cholesterol efflux, a necessary event before capacitation - and subsequent fertilization - can occur. The binding of phosphorylcholine (PrC) and lysophosphatidylcholine (Lyso-PC) with PDC-109 was investigated by monitoring the ligand-induced changes in the absorption spectrum of PDC-109. At 20 degrees C, the association constants (K(a)), for PrC and Lyso-PC were obtained as 81.4M(-1) and 2.02 x 10(4) M(-1), respectively, indicating that the binding of Lyso-PC to PDC-109 is 250-fold stronger than that of PrC. From the temperature dependence of the K(a) values, enthalpy of binding (DeltaH(0)) and entropy of binding (DeltaS(0)), were obtained as -79.7 and -237.1 J mol(-1)K(-1) for PrC and -73.0 kJ mol(-1) and -167.3 J mol(-1)K(-1) for Lyso-PC, respectively. These results demonstrate that although the binding of these two ligands is driven by enthalpic forces, smaller negative entropy of binding associated with Lyso-PC results in its significantly stronger binding.
Anbazhagan
V
V
School of Chemistry, University of Hyderabad, India.
Swamy
Musti J
MJ
D000818:Animals; D002417:Cattle; D002942:Circular Dichroism; D008244:Lysophosphatidylcholines / Q000378:metabolism*; D008297:Male; D010767:Phosphorylcholine / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D012661:Semen / Q000378:metabolism*; D029607:Seminal Vesicle Secretory Proteins / Q000737:chemistry / Q000378:metabolism*; D013056:Spectrophotometry, Ultraviolet; D013816:Thermodynamics
D008244:Lysophosphatidylcholines; D029607:Seminal Vesicle Secretory Proteins; C424303:seminal vesicle secretory protein 109, Bos taurus; D010767:Phosphorylcholine