PKC epsilon has an alcohol-binding site in its second cysteine-rich regulatory domain.
Alcohols regulate the expression and function of PKC (protein kinase C), and it has been proposed that an alcohol-binding site is present in PKC alpha in its C1 domain, which consists of two cysteine-rich subdomains, C1A and C1B. A PKC epsilon-knockout mouse showed a significant decrease in alcohol consumption compared with the wild-type. The aim of the present study was to investigate whether an alcohol-binding site could be present in PKC epsilon. Here we show that ethanol inhibited PKC epsilon activity in a concentration-dependent manner with an EC50 (equilibrium ligand concentration at half-maximum effect) of 43 mM. Ethanol, butanol and octanol increased the binding affinity of a fluorescent phorbol ester SAPD (sapintoxin-D) to PKC epsilon C1B in a concentration-dependent manner with EC50 values of 78 mM, 8 mM and 340 microM respectively, suggesting the presence of an allosteric alcohol-binding site in this subdomain. To identify this site, PKC epsilon C1B was photolabelled with 3-azibutanol and 3-azioctanol and analysed by MS. Whereas azibutanol preferentially labelled His236, Tyr238 was the preferred site for azioctanol. Inspection of the model structure of PKC epsilon C1B reveals that these residues are 3.46 A (1 A=0.1 nm) apart from each other and form a groove where His236 is surface-exposed and Tyr238 is buried inside. When these residues were replaced by alanine, it significantly decreased alcohol binding in terms of both photolabelling and alcohol-induced SAPD binding in the mutant H236A/Y238A. Whereas Tyr238 was labelled in mutant H236A, His236 was labelled in mutant Y238A. The present results provide direct evidence for the presence of an allosteric alcohol-binding site on protein kinase C epsilon and underscore the role of His236 and Tyr238 residues in alcohol binding.
Das
Joydip
J
Department of Pharmacological and Pharmaceutical Sciences, College of Pharmacy, University of Houston, Houston, TX 77204, USA. jdas@uh.edu
Pany
Satyabrata
S
Rahman
Ghazi M
GM
Slater
Simon J
SJ
D000437:Alcoholism / Q000378:metabolism*; D000438:Alcohols / Q000378:metabolism*; D000595:Amino Acid Sequence; D001665:Binding Sites; D003460:Crystallization; D006801:Humans; D007700:Kinetics; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D009154:Mutation; D011485:Protein Binding; D011487:Protein Conformation; D051744:Protein Kinase C-epsilon / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
D000438:Alcohols; D011994:Recombinant Proteins; D051744:Protein Kinase C-epsilon