Oxidation driven surface hydrophobicity in human seminal plasma results in protein structural changes

Abstract

Oxidative stress induced changes in conformational properties of proteins are potential causes of functional impairment in protein system. This phenomenon becomes an important study area when the affected proteins present a role in disease aetiology. The current study was aimed at studying seminal plasma protein conformation changes under higher Reactive oxygen species levels. A total of 100 semen samples (control: n = 50 and infertile n = 50) were used after routine semen parameter analysis. Samples were analysed for their total protein content, ROS levels, total antioxidant capacity and polyacrylamide gel electrophoresis was performed under native conditions. A protein band of molecular weight less than 14 KDa was seen differentially in infertile sample presented with higher ROS levels(>72.6 μg formazan/107 sperm cells). MALDI analysis identified the protein to be Tumor Necrosis Factor alpha super family 18 (TNFα-18) ligand. Further analysis of biophysical properties of the protein showed a significant increase in surface hydrophobicity. Binding of seminal plasma TNFα-18 with ANS dye resulted in an increased fluorescence and broadening of emission curves in infertile samples. Changes in structural properties of TNFα-18ligand prevented it from forming stable oligomeric structures which are essential for effective functioning of the protein.