Schmitt M C, Jamison R S, Orgebin-Crist M C, Ong D E
Department of Biochemistry, Vanderbilt University, Nashville, Tennessee 37232.
Biol Reprod. 1994 Aug;51(2):239-45. doi: 10.1095/biolreprod51.2.239.
A novel member of the cellular lipophilic transport protein superfamily was identified after an antiserum raised against cellular retinoic acid-binding protein (CRABP) was found also to contain antibodies against another 15-kDa protein present in the cytosol of pubertal and adult rat testis. These antibodies were used to screen a rat testis cDNA expression library and isolate a 561-bp clone containing a full open reading frame from which the sequence of a novel 132 amino acid protein was deduced. The protein has 58% amino acid sequence identity to bovine myelin P2, 58% identity to murine adipocyte lipid-binding protein, and 40% identity to rat CRABP. Although the endogenous ligand has not yet been identified, conservation of residues involved in the binding of carboxylate groups suggests that the ligand is a fatty acid or an acidic retinoid. Tissue-specific expression was examined by Northern analysis and immunolocalization and appears to be restricted to late germ cells within the testis and epididymis. Immunostaining was first detectable in mid-pachytene spermatocytes and increased in intensity as these cells progressed to elongated spermatids, suggesting that this testis lipid-binding protein has a specific role in sperm development.
在用针对细胞视黄酸结合蛋白（CRABP）产生的抗血清进行检测时，发现了细胞亲脂性转运蛋白超家族的一个新成员，该抗血清还含有针对青春期和成年大鼠睾丸细胞质中另一种15 kDa蛋白的抗体。这些抗体被用于筛选大鼠睾丸cDNA表达文库，并分离出一个561 bp的克隆，其中包含一个完整的开放阅读框，由此推导出一种新的132个氨基酸的蛋白质序列。该蛋白与牛髓磷脂P2的氨基酸序列一致性为58%，与小鼠脂肪细胞脂质结合蛋白的一致性为58%，与大鼠CRABP的一致性为40%。虽然尚未鉴定出内源性配体，但参与羧基结合的残基的保守性表明该配体是一种脂肪酸或酸性类视黄醇。通过Northern分析和免疫定位研究了组织特异性表达，结果显示其似乎仅限于睾丸和附睾内的晚期生殖细胞。免疫染色最早在粗线期中期精母细胞中可检测到，并随着这些细胞发育为伸长的精子细胞而强度增加，这表明这种睾丸脂质结合蛋白在精子发育中具有特定作用。
