Seminalplasmin, a new protein inhibitor of microbial growth and of transcription from bovine seminal plasma, and two other proteins of seminal plasma

P M BHARGAVA, E S P REDDY, VEEN A N RAO & K H SCHEIT

Published in: Biomolecular structure, Confornation & FunctionI, Ed. R Srinivasan, Pergamon Press, London, 1980, 2, 177-189.

Abstract:

In bovine seminalplasma we have shown the presence of the following three proteins .which appear to possess a hitherto undescribed set of unusual properties.

(1) Seminalplasmin. This protein, purified to homogeneity, is highly bacteriocidal; 20 μg of this protein per millilitre is sufficient to kill virtually all the organisms in a culture of Escherichia coli that has an A760 of 0.01 (~ 107 cells). For 50% inhibition of maximum growth in a synthetic medium under the usual conditions, starting from the above initial cell number, a concentration of approximately 5-10μg/ml is sufficient. The bacteriocidal effect of this protein is apparently due to specific inhibition of the synthesis of rRNA; the synthesis of tRNA and of at least the bulk of mRNA is not inhibited significantly at concentrations (even as high as 100 μg/ml) that inhibit rRNA synthesis almost completely. Seminalplasmin appears to be the third antimicrobial protein from a mammalian source (the other two being lysozyme and β-lysin), and the first protein shown to act as a specific inhibitor of rRNA synthesis in vivo. Seminalplasmin exercises its inhibitory action by entering the cell, and is the first antimicrobial protein after colicin E3, shown to enter a bacterial cell; however, in contrast to colicin E3, seminalplasmin does not require the presence of specific receptors at the cell surface. This protein is also an inhibitor of transcription in vitro where too it appears to show some specificity in regard to the inhibition, as in vivo.

(2) Seminalplasma ribonuclease. This ribonuclease has been purified to homogeneity. It is, like RNAase A, pyrimidine specific. It hydrolyses both single and double-stranded polyribonucleotides possessing susceptible bonds. The rate of hydrolysis on the species is less than that on the former, only by a factor of2. It exhibits the rather peculiar property of strongly reduced rate of hydrolysis on native RNA, such as total E. coli RNA or total rat-liver RNA, quite in contrast to RNAase A. On the other hand, its activity on unstructured oligo- and polyribonucleotides is so high that, in an in vitro transcribing system, it breaks down the transcription products at the rate at which they are formed and, thus, appears to act as a potent inhibitor of transcription even at extremely low concentrations of the order of a microgram per millilitre.

(3) Antiseminalplasmin. This protein, not yet purified to homogeneity, inhibits the bacterial-growth inhibitory activity of seminalplasmin.

HOW TO CITE

Seminalplasmin, a new protein inhibitor of microbial growth and of transcription from bovine seminal plasma, and two other proteins of seminal plasma. P M BHARGAVA, E S P REDDY, VEEN A N RAO & K H SCHEIT. Biomolecular structure, Confornation & FunctionI, Ed. R Srinivasan, Pergamon Press, London, 1980, 2, 177-189.

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