Burne R A, Penders J E
Department of Dental Research, University of Rochester Medical Center, New York 14642.
Infect Immun. 1992 Nov;60(11):4621-32. doi: 10.1128/iai.60.11.4621-4632.1992.
The complete nucleotide sequence (5,010 bp) of the fructanase gene (fruA) and flanking regions of the chromosome of Streptococcus mutans GS-5 was determined. The fruA gene appears to be the sole transcript arising from a proximal promoter. The presumed precursor of the secreted FruA protein consists of 1,423 amino acids, and it has an M(r) of 158,656 and a pI of 4.82. The N terminus of FruA has characteristics in common with signal peptides of gram-positive organisms. The C terminus consists of a serine- and threonine-rich region, followed by the peptide LPDTGD, 4 charged amino acids, 21 amino acids with a strongly hydrophobic character, and a charged pentapeptide tail, which are proposed to correspond to the wall-spanning region, the LPXTGX consensus sequence, and the membrane-spanning domains of surface-associated proteins of gram-positive cocci. The FruA protein has significant homology with the Bacillus subtilis levanase (SacC), the Bacteroides fragilis levanase (ScrL), yeast invertases, and a number of other beta-fructosidases but not with fructosyltransferase, glucosyltransferases, or glucan-binding proteins of oral streptococci. Genes with homology to fruA were detected in S. mutans serotype c, e, and f strains, Streptococcus rattus, Streptococcus salivarius, and Streptococcus sanguis. A deletion derivative of FruA lacking the C-terminal 437 amino acids was still functional and could hydrolyze beta-(2,6)- and beta-(2,1)-linked sugars, but with altered preference for substrates. The data begin to define functional domains of the FruA protein and potential regulatory sites for induction, repression, growth rate control, and posttranslational localization of this multifunctional enzyme.
测定了变形链球菌GS-5染色体上果聚糖酶基因（fruA）及其侧翼区域的完整核苷酸序列（5010 bp）。fruA基因似乎是由近端启动子产生的唯一转录本。推测的分泌型FruA蛋白前体由1423个氨基酸组成，其分子量为158656，等电点为4.82。FruA的N端具有革兰氏阳性菌信号肽的共同特征。C端由富含丝氨酸和苏氨酸的区域组成，接着是肽LPDTGD、4个带电荷的氨基酸、21个具有强疏水性的氨基酸以及一个带电荷的五肽尾，这些被认为分别对应革兰氏阳性球菌表面相关蛋白的跨壁区域、LPXTGX共有序列和跨膜结构域。FruA蛋白与枯草芽孢杆菌果聚糖酶（SacC）、脆弱拟杆菌果聚糖酶（ScrL）、酵母转化酶以及许多其他β-果糖苷酶具有显著同源性，但与口腔链球菌的果糖基转移酶、葡糖基转移酶或葡聚糖结合蛋白没有同源性。在变形链球菌c、e和f血清型菌株、鼠链球菌、唾液链球菌和血链球菌中检测到了与fruA同源的基因。缺失C端437个氨基酸的FruA缺失衍生物仍具有功能，能够水解β-(2,6)-和β-(2,1)-连接的糖，但对底物的偏好有所改变。这些数据开始界定FruA蛋白的功能结构域以及该多功能酶诱导、阻遏、生长速率控制和翻译后定位的潜在调控位点。
