Vadeboncoeur C, Gauthier L, Gagnon G, Leduc A, Brochu D, Lapointe R, Desjardins B, Frenette M
Department of Biochemistry (Sciences) and Faculty of Dentistry, Université Laval, Québec, Canada.
J Bacteriol. 1994 Jan;176(2):524-7. doi: 10.1128/jb.176.2.524-527.1994.
HPr is a protein of the phosphoenolpyruvate:sugar phosphotransferase system (PTS) that participates in the concomitant transport and phosphorylation of sugars in bacteria. In gram-positive bacteria, HPr is also reversibly phosphorylated at a seryl residue at position 46 (Ser-46) by a metabolite-activated ATP-dependent kinase and a Pi-dependent HPr(Ser-P) phosphatase. We report in this article the isolation of a spontaneous mutant (mutant A66) from a streptococcus (Streptococcus salivarius) in which the methionine at position 48 (Met-48) in the protein HPr has been replaced by a valine (Val). The mutation inhibited the phosphorylation of HPr on Ser-46 by the ATP-dependent kinase but did not prevent phosphorylation of HPr by enzyme I or the phosphorylation of enzyme II complexes by HPr(His-P). The results, however, suggested that replacement of Met-48 by Val decreased the affinity of enzyme I for HPr or the affinity of enzyme II proteins for HPr(His-P) or both. Characterization of mutant A66 demonstrated that it has pleiotropic properties, including the lack of IIILman, a specific protein of the mannose PTS; decreased levels of HPr; derepression of some cytoplasmic proteins; reduced growth on PTS as well as on non-PTS sugars; and aberrant growth in medium containing a mixture of sugars.
HPr是磷酸烯醇丙酮酸：糖磷酸转移酶系统（PTS）中的一种蛋白质，参与细菌中糖的伴随运输和磷酸化。在革兰氏阳性细菌中，HPr还可被代谢物激活的ATP依赖性激酶和Pi依赖性HPr（Ser-P）磷酸酶在第46位丝氨酸残基（Ser-46）处进行可逆磷酸化。我们在本文中报道了从唾液链球菌中分离出的一个自发突变体（突变体A66），其中蛋白质HPr中第48位的甲硫氨酸（Met-48）被缬氨酸（Val）取代。该突变抑制了ATP依赖性激酶对HPr在Ser-46处的磷酸化，但不阻止酶I对HPr的磷酸化或HPr（His-P）对酶II复合物的磷酸化。然而，结果表明，Val取代Met-48降低了酶I对HPr的亲和力或酶II蛋白对HPr（His-P）的亲和力，或两者均降低。突变体A66的特征表明它具有多效性，包括缺乏甘露糖PTS的特异性蛋白IIILman；HPr水平降低；一些细胞质蛋白的去阻遏；在PTS糖以及非PTS糖上的生长减少；以及在含有混合糖的培养基中生长异常。
