Kriakov Jordan, Lee Sun hee, Jacobs William R
Department of Microbiology and Immunology, Howard Hughes Medical Institute, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
J Bacteriol. 2003 Aug;185(16):4983-91. doi: 10.1128/JB.185.16.4983-4991.2003.
Although alkaline phosphatases are common in a wide variety of bacteria, there has been no prior evidence for alkaline phosphatases in Mycobacterium smegmatis. Here we report that transposon insertions in the pst operon, encoding homologues of an inorganic phosphate transporter, leads to constitutive expression of a protein with alkaline phosphatase activity. DNA sequence analysis revealed that M. smegmatis does indeed have a phoA gene that shows high homology to other phoA genes. The M. smegmatis phoA gene was shown to be induced by phosphate starvation and thus negatively regulated by the pst operon. Interestingly, the putative M. smegmatis PhoA has a hydrophobic N-terminal domain which resembles a lipoprotein signal sequence. The M. smegmatis PhoA was demonstrated to be an exported protein associated with the cell surface. Furthermore, immunoprecipitation of PhoA from [(14)C]acetate-labeled M. smegmatis cell lysates demonstrated that this phosphatase is a lipoprotein.
尽管碱性磷酸酶在多种细菌中普遍存在，但此前尚无耻垢分枝杆菌中存在碱性磷酸酶的证据。在此我们报告，编码无机磷酸盐转运蛋白同源物的pst操纵子中的转座子插入，导致具有碱性磷酸酶活性的蛋白质组成型表达。DNA序列分析表明，耻垢分枝杆菌确实有一个与其他phoA基因具有高度同源性的phoA基因。耻垢分枝杆菌phoA基因被证明受磷酸盐饥饿诱导，因此受pst操纵子负调控。有趣的是，推测的耻垢分枝杆菌PhoA具有一个类似于脂蛋白信号序列的疏水N端结构域。耻垢分枝杆菌PhoA被证明是一种与细胞表面相关的分泌蛋白。此外，从[(14)C]乙酸盐标记的耻垢分枝杆菌细胞裂解物中免疫沉淀PhoA，证明这种磷酸酶是一种脂蛋白。
