Strain-Dependent Recognition of a Unique Degradation Motif by ClpXP in Streptococcus mutans.
Strain-Dependent Recognition of a Unique Degradation Motif by ClpXP in Streptococcus mutans.
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DOI：
10.1128/msphere.00287-16
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发表时间：
2016-11
期刊：
影响因子：
4.8
通讯作者：
Biswas I
中科院分区：
文献类型：
--
作者：
Jana B;Tao L;Biswas I
细菌中的调节性蛋白质水解是维持蛋白质稳态的重要生物学过程。ClpXP是一种细胞内蛋白水解复合物，是负责蛋白质周转的主要蛋白酶。虽然在大肠杆菌中鉴定了ClpXP的底物，但绝大多数细菌的底物目前尚不清楚。在这项研究中，我们确定了一个独特的基板ClpXP介导的降解变形链球菌，牙齿病原体。我们还发现，由3个氨基酸组成的小基序足以用于ClpXP介导的降解。该基序的鉴定将清楚地帮助我们理解该生物体和其他相关病原体的发病机制。变形链球菌是一种牙源性致病菌，具有显著的科普环境胁迫能力。在胁迫条件下，细胞质蛋白酶在控制调节蛋白的稳定性和防止受损和错误折叠的蛋白质的积累中起主要作用。ClpXP是一种高度保守的细胞质蛋白水解系统，在维持细菌细胞内稳态中至关重要。ClpX主要负责底物的识别和随后将未折叠的底物易位到ClpP蛋白水解区室中进行降解。在大肠杆菌中，ClpX识别存在于靶蛋白C末端的不同基序。然而，ClpXP在其他细菌（包括变形链球菌）中的识别序列是未知的。在这项研究中，使用二维（2D）聚丙烯酰胺凝胶电泳（PAGE）分析，我们已经确定了变形链球菌ClpXP的几个假定的底物。SsbA编码一种小DNA结合蛋白，是被ClpXP降解的底物之一。通过连续缺失，我们发现最后3个C末端氨基酸LPF足以用于ClpXP介导的降解。在绿色荧光蛋白（GFP）的C-末端添加LPF使得蛋白质可被ClpXP完全降解。这种三肽基序的改变阻碍了ClpXP介导的降解。然而，ClpXP对LPF的识别对一些变形链球菌菌株（UA 159、UA 130和N3209）具有高度特异性，因为并非所有变形链球菌菌株都识别该基序。我们推测，衔接蛋白参与底物识别或底物降解ClpXP。尽管如此，这是第一次报道链球菌中ClpXP的独特识别序列。细菌中的调节性蛋白水解是维持蛋白质稳态的重要生物学过程。ClpXP是一种细胞内蛋白水解复合物，是负责蛋白质周转的主要蛋白酶。虽然在大肠杆菌中鉴定了ClpXP的底物，但绝大多数细菌的底物目前尚不清楚。在这项研究中，我们确定了一个独特的基板ClpXP介导的降解变形链球菌，牙齿病原体。我们还发现，由3个氨基酸组成的小基序足以用于ClpXP介导的降解。该基序的鉴定将清楚地帮助我们理解该生物体和其他相关病原体的发病机制。
Regulated proteolysis in bacteria is an important biological process that maintains protein homeostasis. ClpXP, an intracellular proteolytic complex, is the primary protease that is responsible for protein turnover. While the substrates for ClpXP were identified in Escherichia coli, the substrates for vast majority of bacteria are currently unknown. In this study, we identified a unique substrate for ClpXP-mediated degradation in Streptococcus mutans, a dental pathogen. We also found that a small motif composed of 3 amino acids is sufficient for ClpXP-mediated degradation. Identification of this motif will clearly help us to understand the pathogenesis of this organism and other related pathogens. Streptococcus mutans, a dental pathogen, has a remarkable ability to cope with environmental stresses. Under stress conditions, cytoplasmic proteases play a major role in controlling the stability of regulatory proteins and preventing accumulation of damaged and misfolded proteins. ClpXP, a well-conserved cytoplasmic proteolytic system, is crucial in maintaining cellular homeostasis in bacteria. ClpX is primarily responsible for recognition of substrates and subsequent translocation of unfolded substrates into the ClpP proteolytic compartment for degradation. In Escherichia coli, ClpX recognizes distinct motifs present at the C-terminal end of target proteins. However, recognition sequences for ClpXP in other bacteria, including S. mutans, are not known. In this study, using two-dimensional (2D) polyacrylamide gel electrophoresis (PAGE) analysis, we have identified several putative substrates for S. mutans ClpXP. SsbA, which encodes a small DNA binding protein, is one such substrate that is degraded by ClpXP. By sequential deletions, we found that the last 3 C-terminal amino acids, LPF, are sufficient for ClpXP-mediated degradation. Addition of LPF at the C-terminal end of green fluorescent protein (GFP) rendered the protein completely degradable by ClpXP. Alterations of this tripeptide motif impeded ClpXP-mediated degradation. However, recognition of LPF by ClpXP is highly specific to some S. mutans strains (UA159, UA130, and N3209) since not all S. mutans strains recognize the motif. We speculate that an adaptor protein is involved in either substrate recognition or substrate degradation by ClpXP. Nevertheless, this is the first report of a unique recognition sequence for ClpXP in streptococci. IMPORTANCE Regulated proteolysis in bacteria is an important biological process that maintains protein homeostasis. ClpXP, an intracellular proteolytic complex, is the primary protease that is responsible for protein turnover. While the substrates for ClpXP were identified in Escherichia coli, the substrates for vast majority of bacteria are currently unknown. In this study, we identified a unique substrate for ClpXP-mediated degradation in Streptococcus mutans, a dental pathogen. We also found that a small motif composed of 3 amino acids is sufficient for ClpXP-mediated degradation. Identification of this motif will clearly help us to understand the pathogenesis of this organism and other related pathogens.