Structural modelling of the equine protein disulphide isomerase A1 and its quantification in the epididymis and seminal plasma.

The protein disulphide isomerase A1 (PDIA1) is an important chaperone involved in protein quality control and redox regulation. Also, the ability of PDIA1 to bind to oestrogens suggests that it may play a role in epididymal maturation and male fertility. The goals of this study were to (a) verify the possible interaction between 17β-estradiol and equine PDIA1 using bioinformatics; (b) identify and quantify PDIA1 protein in equine cauda epididymis throughout peripuberty; and (c) determine whether the amounts of PDIA1 in equine seminal plasma and spermatozoa are associated with fertility. Using in silico analysis, we were able to predict the tertiary structure of equine PDIA1 and to demonstrate the interaction between 17β-estradiol and the putative binding site in domains b and b'. Colts under 24 months of age had lower relative amounts of PDIA1 in cauda epididymal fluid in comparison with older males (p < .01). No difference was observed in seminal plasma PDIA1 between fertile and subfertile stallions. Our study demonstrates that PDIA1 expression in the epididymis increases during peripuberty. However, in the adult stallion, its quantity in seminal plasma is not associated with fertility.