HlyC, the internal protein acyltransferase that activates hemolysin toxin: the role of conserved tyrosine and arginine residues in enzymatic activity as probed by chemical modification and site-directed mutagenesis.
Internal fatty acylation of proteins is a recognized means of modifying biological behavior. Escherichia coli hemolysin A (HlyA), a toxic protein, is transcribed as a nontoxic protein and made toxic by internal acylation of two lysine residue epsilon-amino groups; HlyC catalyzes the acyl transfer from acyl-acyl carrier protein (ACP), the obligate acyl donor. Conserved residues among the respective homologous C proteins that activate 13 different RTX (repeats in toxin) toxins of which HlyA is the prototype likely include some residues that are important in catalysis. Possible roles of two conserved tyrosines and two conserved arginines were investigated by noting the effects of chemical modifiers and site-directed mutagenesis. TNM modification of HlyC at pH 8.0 led to extensive inhibition that was prevented by the presence of the substrate myristoyl-ACP but not by the product, ACPSH. NAI had no effect. Y70G and Y150G greatly diminished enzyme activity, whereas mutations Y70F and Y150F exhibited wild-type activity. Modification of arginine residues with PG markedly lowered acyltransferase activity with moderate protection by both myristoyl-ACP and ACPSH. Under optimum conditions, four separate mutations of the two conserved arginine residues (R24A, R24K, R87A, and R87K) had little effect on acyltransferase activity.
Trent
M S
MS
Department of Biochemistry and Molecular Biology, James H. Quillen College of Medicine, East Tennessee State University, Johnson City 37614, USA.
Worsham
L M
LM
Ernst-Fonberg
M L
ML
D000123:Acetyltransferases / Q000737:chemistry* / Q000235:genetics / Q000502:physiology; D000217:Acyltransferases; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000235:genetics; D001120:Arginine / Q000737:chemistry* / Q000235:genetics; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000502:physiology; D001427:Bacterial Toxins / Q000737:chemistry* / Q000235:genetics; D004789:Enzyme Activation / Q000235:genetics; D004926:Escherichia coli; D029968:Escherichia coli Proteins; D006460:Hemolysin Proteins / Q000737:chemistry* / Q000235:genetics / Q000502:physiology; D007093:Imidazoles / Q000737:chemistry; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010658:Phenylglyoxal / Q000737:chemistry; D013439:Sulfhydryl Reagents / Q000737:chemistry; D013774:Tetranitromethane / Q000737:chemistry; D014443:Tyrosine / Q000737:chemistry* / Q000235:genetics
D001426:Bacterial Proteins; D001427:Bacterial Toxins; D029968:Escherichia coli Proteins; D006460:Hemolysin Proteins; D007093:Imidazoles; D013439:Sulfhydryl Reagents; D014443:Tyrosine; D001120:Arginine; D000217:Acyltransferases; D000123:Acetyltransferases; C092237:HlyC protein, E coli; C062782:protein acyltransferase; D013774:Tetranitromethane; D010658:Phenylglyoxal; C012160:N-acetylimidazole