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In this article we will focus on the structure of carnitine acetyltransferase as a representitive of carnitine acyltransferases. Determining the structure and thus the molecular basis for fatty acid transfer is needed for drug development.Being major enzymes in fatty acid oxidation carnitine acyltransferases  are viewed as promising targets which can be used to develop successful therapeutics against type 2 diabetes, obesity and other human diseases.  

The carnitine acyltransferases have important biological functions.All members of carnitine acyltransferases catalyze the same reversible reaction:the exchange of acyl groups between carnitine and coenzyme A (CoA)--> see picture. This is in accord with the fact, that the catalytic domains of all the carnitine acyltransferases are well conserved.

The most important biological function of carnitine acyltransferases is the transport of fatty acids for β-oxidation(2).Fatty acids are oxidized for energy production in the mitochondrial matrix by a process called β- oxidation. The major site of fatty acid accumulation, however, is the cytoplasm of the cells. Hence, in order to provide energy, fatty acids have to be transported from the cytoplasm across the inner mitochondrial membrane into the mitochondrial matrix. The carnitine shuttle , a transport chain that consists of three enzymatic reactions, helps fatty acids to pass the mitochondrial membrane. Carnitine acyltransferases (CrATs, CrOTs, CPTs) are part of the carnitine shuttle. The first step of the carnitine shuttle is the activation of fatty acids. They are transformed into the activated form (= acyl CoA) by the formation of a thioester linkage between the fatty acid carboxyl group and the thiol group of coenzyme A. The second step of the carnitine shuttle is catalyzed by carnitine acyltransferases I. These enzymes (especially CPT I) facilitate the transport of fatty acids by conjugating them to carnitine. In this reaction an acyl group (make orange)is transferred from the sulfur atom of CoA to the hydroxyl group of carnitine. The product is form acyl -carnitine.  

The third step of the carnitine shuttle is catalyzed by carnitine acyl transferases II (especially CPT II) in teh mitochondrial matrix. In this reaction the acyl group of acyl- carnitine is transferred back to CoA to form acetyl- CoA by carnitine acyl transferases II found in the matrix.