Submitted September 11, 2007
Returned for revision November 22, 2007
Accepted January 9, 2008
Male Reproductive Tract
Molecular and Functional Characterization of the Rabbit Epididymal Secretory Protein 52, REP52
Brett Nixon *,
Russell C. Jones ,
and
Michael K. Holland
* To whom correspondence should be addressed. E-mail: brett.nixon{at}newcastle.edu.au.
Abstract
As part of a systematic study of rabbit epididymal proteins involved in sperm maturation we have identified and characterised a novel glycoprotein (REP52) of 52 kDa. REP52 is synthesised and secreted in a tissue-specific manner by the mid (region 6) and distal (region 7) corpus epididymidis and associates weakly with the sperm surface overlying the principal piece of the tail. Sequencing of cloned REP52 cDNA demonstrated that this protein represents a novel member of the highly conserved fibronectin type II (Fn2)-module protein family. The protein appears related but not homologous to ungulate seminal plasma proteins, and is the first known example to be identified as a rabbit epididymal secretory protein. Consistent with other members of this protein family, REP52 possessed a high level of sequence identity within the Fn2-module-encoding domains, but a highly variable N-terminal sequence that failed to show significant homology with published sequences. By analogy with evidence from studies of the ungulate seminal plasma proteins it is hypothesized that the tandemly arranged Fn2-modules could facilitate the association of REP52 with sperm phosphatidylcholine residues on the outer leaflet of the sperm tail. It is also considered likely that these domains represents key elements for the function of this novel protein, a conclusion supported by the fact that antisera raised against the REP52 protein blocked in vitro fertilization in a concentration dependent fashion.
Key words:
Male Reproductive Tract •
Epididymis •
Sperm maturation
