Immunological crossreactivity to the catabolite control protein CcpA from Bacillus megaterium is found in many Gram-positive bacteria

Abstract The catabolite control protein CcpA from Bacillus megaterium was overproduced as a fusion protein to a 6xhis affinity tag and purified to homogeneity. Polyclonal antibodies of high affinity and specificity were raised against the purified protein. The serum did not crossreact with purified Lac repressor despite the fact that CcpA and LacI belong to the same protein family. Using this antiserum we identified proteins that share antigenic determinants with CcpA in many Gram-positive bacteria, including bacilli, staphylococci, streptococci, lactic acid bacteria, and some actinomycetes.     

Regulators of the Bacillus subtilis cydABCD operon: identification of a negative regulator, CcpA, and a positive regulator, ResD

The cydABCD operon of Bacillus subtilis encodes products required for the production of cytochrome bd oxidase. Previous work has shown that one regulatory protein, YdiH (Rex), is involved in the repression of this operon. The work reported here confirms the role of Rex in the negative regulation of the cydABCD operon. Two additional regulatory proteins for the cydABCD operon were identified, namely, ResD, a response regulator involved in the regulation of respiration genes, and CcpA, the carbon catabolite regulator protein. ResD, but not ResE, was required for full expression of the cydA promoter in vivo. ResD binding to the cydA promoter between positions -58 and -107, a region which includes ResD consensus binding sequences, was not enhanced by phosphorylation. A ccpA mutant had increased expression from the full-length cydA promoter during stationary growth compared to the wild-type strain. Maximal expression in a ccpA mutant was observed from a 3'-deleted cydA promoter fusion that lacked the Rex binding region, suggesting that the effect of the two repressors, Rex and CcpA, was cumulative. CcpA binds directly to the cydA promoter, protecting the region from positions -4 to -33, which contains sequences similar to the CcpA consensus binding sequence, the cre box. CcpA binding was enhanced upon addition of glucose-6-phosphate, a putative cofactor for CcpA. Mutation of a conserved residue in the cre box reduced CcpA binding 10-fold in vitro and increased cydA expression in vivo. Thus, CcpA and ResD, along with the previously identified cydA regulator Rex (YdiH), affect the expression of the cydABCD operon. Low-level induction of the cydA promoter was observed in vivo in the absence of its regulatory proteins, Rex, CcpA, and ResD. This complex regulation suggests that the cydA promoter is tightly regulated to allow its expression only at the appropriate time and under the appropriate conditions.     

Catabolite repression in Lactobacillus casei ATCC 393 is mediated by CcpA.

The chromosomal ccpA gene from Lactobacillus casei ATCC 393 has been cloned and sequenced. It encodes the CcpA protein, a central catabolite regulator belonging to the LacI-GalR family of bacterial repressors, and shows 54% identity with CcpA proteins from Bacillus subtilis and Bacillus megaterium. The L. casei ccpA gene was able to complement a B. subtilis ccpA mutant. An L. casei ccpA mutant showed increased doubling times and a relief of the catabolite repression of some enzymatic activities, such as N-acetylglucosaminidase and phospho-beta-galactosidase. Detailed analysis of CcpA activity was performed by using the promoter region of the L. casei chromosomal lacTEGF operon which is subject to catabolite repression and contains a catabolite responsive element (cre) consensus sequence. Deletion of this cre site or the presence of the ccpA mutation abolished the catabolite repression of a lacp::gusA fusion. These data support the role of CcpA as a common regulatory element mediating catabolite repression in low-GC-content gram-positive bacteria.     

Identification of a co-repressor binding site in catabolite control protein CcpA

The catabolite control protein CcpA is the central regulator of carbon catabolite repression in Bacilli and other Gram-positive bacteria. A comparison of 12 CcpA-like sequences with regulators from the LacI/GalR family defines a CcpA subfamily based on extensive similarities found among CcpAs and not in 32 other members of the family. These amino acids are clustered in three blocks in the CcpA sequence. Their interpretation, assuming a PurR-like fold, reveals that almost all of them are surface exposed and form a continuous patch on the N-terminal subdomain of the protein core extending into the DNA reading head. We introduced nine single amino acid exchanges in the subfamily specific residues of CcpA from Bacillus megaterium . Six mutants, namely CcpA47RS, 79AE, 89YE, 295YR, 299YE and 303RD, are inactive or severely impaired in catabolite repression, underlining their relevance for CcpA function. They are negatively transdominant over wild-type CcpA demonstrating their ability to correctly fold for dimerization. Five of them are unable or impaired in binding HPr-Ser-46-P in vitro , establishing a correlation between catabolite repression efficiency and HPr-Ser-46-P binding. These results support the hypothesis that the conserved region in CcpA is the HPr-Ser-46-P binding site.     

CcpA mutants with differential activities in Bacillus subtilis

CcpA is the master regulator for carbon catabolite regulation in Bacillus subtilis and regulates more than 300 genes by repression or activation. To revealthe effects of different functional domains of CcpA on various regulatory modes, we compared the activities of CcpA point mutants in activation (alsS, ackA) and repression (xynP, gntR). CcpA variants mutated at residues in the HPrSerP-binding region without allosteric functions are inactive. On the other hand, CcpA variants mutated at residues that change their conformation upon HPrSerP or CrhP binding regulate only ackA. Another set of mutants with alterations in the corepressor-binding region show glucose-independent regulation of xynP. The data presented here demonstrate the involvement of HPrSerP and/or CrhP in activation of ackA and alsS by CcpA. Furthermore, these data also indicate that activation and repression mediated by CcpA may utilize different conformational changes of the protein.     

Residues His-15 and Arg-17 of HPr participate differently in catabolite signal processing via CcpA

The carbon catabolite control protein A (CcpA) senses the physiological state of the cell by binding several effectors and responds with differential regulation of many genes in Bacilli. HPr-Ser46-P or Crh-Ser46-P interact with CcpA and stimulate binding to catabolite responsive elements. In addition, the glycolytic intermediates fructose 1,6-bisphosphate (FBP) and glucose 6-phosphate (Glc-6-P) stimulate HPr-Ser46-P but not Crh-Ser46-P binding to CcpA. The mechanisms by which coeffector binding to CcpA is linked to differential gene expression are unclear. To address this question we mutated residues participating in the interaction between HPr-Ser46-P or Crh-Ser46-P and CcpA and analyzed their effects on CcpA binding and stimulation of cre binding by surface plasmon resonance. The HPrH15A and CcpAD297A mutations do not affect complex formation but abolish FBP and Glc-6-P stimulation. Likewise, the CrhQ15H mutant becomes sensitive to these glycolytic intermediates. Hence, the contact of HPrHis-15 to Asp-297 in CcpA is a determinant for HPr specific FBP and Glc-6-P stimulation. The HPrR17A and -K mutants are both strongly impaired in stimulation of CcpA binding to cre, but only HPrR17A is defect in binding to CcpA indicating that these residues affect allostery of CcpA. Mutations of the residues of CcpA, which contact Arg-17 of HPr, exhibit differential effects on regulation of catabolic genes. Taken together, His-15 of HPr processes sensing information, while Arg-17 is involved in determining the genetic output.     

单核细胞增生李斯特菌中CcpA缺失株的构建及对毒力的影响

CcpA是革兰氏阳性菌中由ccpA基因编码的介导碳分解代谢物阻遏的全局调控因子。近年来的研究表明,CcpA不仅参与CCR效应,还直接或间接参与病原细菌毒力基因的表达调控。为探讨CcpA对单核细胞增生李斯特菌（Lm）毒力的影响,应用同源重组方法构建CcpA缺失菌株。以BLAB/c小鼠为实验动物模型,检测野生株EGDe和缺失株EGDeΔccpA侵染小鼠后的半数致死剂量 LD₅₀和肝脾细菌载菌量,观察小鼠肝脏和脾脏的病理形态变化。结果显示：缺失CcpA后,Lm的LD₅₀降低了10倍,虽然肝脾细菌载菌量没有显著变化,但EGDe△ccpA对小鼠肝和脾的损害更为严重,表明CcpA缺失增强了细菌的毒力,CcpA 对Lm 毒力基因的表达可能具有间接或者直接的调控作用。