Ventura Marco, Jankovic Ivana, Walker D Carey, Pridmore R David, Zink Ralf
Nestlé Research Center, Vers-Chez-Les-Blanc, 1000 Lausanne 26, Switzerland.
Appl Environ Microbiol. 2002 Dec;68(12):6172-81. doi: 10.1128/AEM.68.12.6172-6181.2002.
We have identified and sequenced the genes encoding the aggregation-promoting factor (APF) protein from six different strains of Lactobacillus johnsonii and Lactobacillus gasseri. Both species harbor two apf genes, apf1 and apf2, which are in the same orientation and encode proteins of 257 to 326 amino acids. Multiple alignments of the deduced amino acid sequences of these apf genes demonstrate a very strong sequence conservation of all of the genes with the exception of their central regions. Northern blot analysis showed that both genes are transcribed, reaching their maximum expression during the exponential phase. Primer extension analysis revealed that apf1 and apf2 harbor a putative promoter sequence that is conserved in all of the genes. Western blot analysis of the LiCl cell extracts showed that APF proteins are located on the cell surface. Intact cells of L. johnsonii revealed the typical cell wall architecture of S-layer-carrying gram-positive eubacteria, which could be selectively removed with LiCl treatment. In addition, the amino acid composition, physical properties, and genetic organization were found to be quite similar to those of S-layer proteins. These results suggest that APF is a novel surface protein of the Lactobacillus acidophilus B-homology group which might belong to an S-layer-like family.
我们已经从六株不同的约氏乳杆菌和加氏乳杆菌中鉴定并测序了编码聚集促进因子（APF）蛋白的基因。这两个菌种都含有两个apf基因，即apf1和apf2，它们方向相同，编码257至326个氨基酸的蛋白质。这些apf基因推导的氨基酸序列的多重比对表明，除了中央区域外，所有基因的序列保守性都很强。Northern印迹分析表明这两个基因都被转录，在指数生长期达到最大表达。引物延伸分析显示apf1和apf2含有一个在所有基因中都保守的推定启动子序列。对LiCl细胞提取物的Western印迹分析表明APF蛋白位于细胞表面。约氏乳杆菌的完整细胞显示出携带S层的革兰氏阳性真细菌的典型细胞壁结构，用LiCl处理可选择性地去除该结构。此外，发现其氨基酸组成、物理性质和基因组织与S层蛋白非常相似。这些结果表明APF是嗜酸乳杆菌B同源组的一种新型表面蛋白，可能属于S层样家族。
