ABSTRACT
Long chain fatty acyl-CoA synthetases are responsible for fatty acid degradation as well as physiological regulation of cellular functions via the production of long chain fatty acyl-CoA esters. We report the first crystal structures of long chain fatty acyl-CoA synthetase homodimer (LC-FACS) from Thermus thermophilus HB8 (ttLC-FACS), including complexes with the ATP analogue adenosine 5'-(beta,gamma-imido) triphosphate (AMP-PNP) and myristoyl-AMP. ttLC-FACS is a member of the adenylate forming enzyme superfamily that catalyzes the ATP-dependent acylation of fatty acid in a two-step reaction. The first reaction step was shown to propagate in AMP-PNP complex crystals soaked with myristate solution. Myristoyl-AMP was identified as the intermediate. The AMP-PNP and the myristoyl-AMP complex structures show an identical closed conformation of the small C-terminal domains, whereas the uncomplexed form shows a variety of open conformations. Upon ATP binding, the fatty acid-binding tunnel gated by an aromatic residue opens to the ATP-binding site. The gated fatty acid-binding tunnel appears only to allow one-way movement of the fatty acid during overall catalysis. The protein incorporates a hydrophobic branch from the fatty acid-binding tunnel that is responsible for substrate specificity. Based on these high resolution crystal structures, we propose a unidirectional Bi Uni Uni Bi Ping-Pong mechanism for the two-step acylation by ttLC-FACS.
Subject(s)
Coenzyme A Ligases/chemistry , Coenzyme A Ligases/metabolism , Adenosine Triphosphate/metabolism , Amino Acid Sequence , Base Sequence , Catalysis , Catalytic Domain , Coenzyme A Ligases/genetics , Crystallography, X-Ray , DNA Primers , DNA, Bacterial/genetics , Dimerization , Models, Molecular , Molecular Sequence Data , Protein Structure, Quaternary , Protein Structure, Tertiary , Recombinant Proteins/chemistry , Recombinant Proteins/genetics , Recombinant Proteins/metabolism , Sequence Homology, Amino Acid , Substrate Specificity , Thermus thermophilus/enzymology , Thermus thermophilus/geneticsABSTRACT
In spite of the common use of the diagnostic category of lichen-planus-like contact dermatitis, we were unable to find established criteria for such a condition. An atypical distribution of otherwise typical lichen planus lesions is usually considered as a feature of a lichenoid eruption. When facing unusual or unexpected clinical features, it is always advisable to consider an adverse reaction to a medical intervention as a potential option. We report a lichen-planus-like eruption occurring after contact with a topical agent containing chlorpheniramine maleate. To our knowledge, this is the first reported case of lichen-planus-like contact dermatitis associated with chlorpheniramine maleate.
