Apolipoprotein A-I binds to a family of bovine seminal plasma proteins

P Manjunath,Y L Marcel,J Uma,N G Seidah,M Chrétien,A Chapdelaine

doi:10.1016/s0021-9258(19)84784-1

P Manjunath, Y L Marcel + Show 4 more

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https://doi.org/10.1016/s0021-9258(19)84784-1

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Abstract

Bovine seminal plasma contains four similar acidic proteins, previously designated as BSP (bovine seminal plasma)-A1, BSP-A2, BSP-A3, and BSP-30-kDa, that when added to pituitary cell cultures result in the immediate secretion of gonadotropins (follitropin and lutropin). However, when calf or horse serum was included in the culture medium the secretion of gonadotropins was completely prevented. This effect was seen at levels up to 200 micrograms of BSP protein/ml while the presence of more than 200 micrograms of BSP protein/ml in the serum medium continued to release gonadotropins. This could be explained by the presence in the sera of a binding factor to the BSP proteins which prevents their action. This binding factor has been detected in all the sera tested, including human serum, in dot-blot experiments using 125I-labeled BSP-A1, -A2, -A3, or -30-kDa protein. Thus, it was of interest to isolate this binding factor from human serum by affinity chromatography on a column of BSP-A1/-A2-agarose. The purified binding factor was then identified as apolipoprotein A-I (apoA-I) by the following criteria: (a) it has a molecular mass of 27,000 daltons, (b) the amino acid composition is similar to apoA-I, (c) the first 25 residues at the amino-terminal end of this binding factor are identical to apoA-I, and (d) the binding factor cross-reacts in the radioimmunoassay of apoA-I. Furthermore, BSP proteins also bind to purified plasma apoA-I and apoA-I associated with high density lipoprotein. ApoA-I is the major protein of plasma high density lipoprotein and plays an important role in lipid transport and metabolism. Thus, the binding of bovine seminal plasma proteins to apoA-I suggests some physiological significance in lipoprotein function or vice versa.

Highlights

From the $Endocrine Laboratory, Maisonneuue-RosemontHospital Research Center and Department of Medicine, Uniuersity of Montreal, and the Laboratories of (Lipoprotein Metabolism, 1)Biochemicaland **Molecular Neuroendocrinology, Clinical
The referred to as gonadotropin release stimulatory and inhibitory proteins [1]. Further characterization of these proteins revealed that the BSP-A1, -A2, and -A3 proteins are identical to thegonadostatins BSP 111,BSP 11, and BSPI, isolated from bovine seminal fluid [5].BSP I1 and BSP 111together are called PDC-109 protein [6], identified as a major protein synthesized and secreted by bull seminal vesicles [7]
Purified binding factor was identified as apolipo- Because the gonadostatins exhibit an antagonistic effect toprotein A-I by the following criteria: (a)it has a molecular mass of 27,000 daltons, ( b )the amino acid composition is similar to apoA-I, (c) the first 25 residues at the amino-terminal end of this binding factor are identical to apoA-I, and ( d ) the binding factor cross-reacts in theradioimmunoassay of apoAI

Summary

Introduction

Bovine seminal plasma contains four similar acidic A2, BSP-AS, and BSP-30-kDa, represents the major acidic proteins, previously designated asBSP (bovineseminal proteins found in bovine seminal fluid (1-31, and they appear plasma)-Al, BSP-AS, BSP-A3, and BSP-30-kDa, that to originate from the seminal vesicles [3, 4] These proteins when added to pituitary cell culturesresultin the stimulate the release of gonadotropins (follitropin and lutroimmediate secretion of gonadotropins (follitropin and lutropin). BSP proteins bind to purified plasma apoA-I and apoA-I associated with high density ward luteinizing hormone-releasing hormone [5] they were once believed to be inhibins [8].sequence studies of gonadostatins [6, 9] as well as ovarian inhibins [10, 11] have clearly demonstrated that they are entirelydifferent proteins.

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