A frequent allele codes for a truncated variant of semenogelin I, the major protein component of human semen coagulum

Abstract

Human semen coagulum predominantly consists of high molecular mass complexes of the seminal vesicle secreted semenogelin I (SgI) and semenogelin II (SgII). Here we describe a previously unknown variant of the SgI gene that is present at an allele frequency of ∼3% in the Swedish population. It gives rise to a protein with a molecular mass of 43 kDa, SgI₄₃, which compared with the 50 kDa variant, SgI₅₀, is lacking a tandem repeat of 60 amino acid residues that was probably deleted by homologous recombination. In spite of the size difference, SgI₄₃ has many properties in common with SgI₅₀, such as a very high iso‐electric point and susceptibility to proteolytic degradation by prostate‐specific antigen. Heterozygous carriers of the SgI₄₃ allele neither show impaired fertility nor do they significantly differ from individuals homozygous for SgI₅₀ with respect to sperm parameters such as semen volume, sperm count and fraction of motile spermatozoa.