Crystal structure of the human acyl protein thioesterase I from a single X-ray data set to 1.5 A.
BACKGROUND
Many proteins undergo posttranslational modifications involving covalent attachment of lipid groups. Among them is palmitoylation, a dynamic, reversible process that affects trimeric G proteins and Ras and constitutes a regulatory mechanism for signal transduction pathways. Recently, an acylhydrolase previously identified as lysophospholipase has been shown to function as an acyl protein thioesterase, which catalyzes depalmitoylation of Galpha proteins as well as Ras. Its amino acid sequence suggested that the protein is evolutionarily related to neutral lipases and other thioesterases, but direct structural information was not available.


RESULTS
We have solved the crystal structure of the human putative Galpha-regulatory protein acyl thioesterase (hAPT1) with a single data set collected from a crystal containing the wild-type protein. The phases were calculated to 1.8 A resolution based on anomalous scattering from Br(-) ions introduced in the cryoprotectant solution in which the crystal was soaked for 20 s. The model was refined against data extending to a resolution of 1.5 A to an R factor of 18.6%. The enzyme is a member of the ubiquitous alpha/beta hydrolase family, which includes other acylhydrolases such as the palmitoyl protein thioesterase (PPT1).


CONCLUSIONS
The human APT1 is closely related to a previously described carboxylesterase from Pseudomonas fluorescens. The active site contains a catalytic triad of Ser-114, His-203, and Asp-169. Like carboxylesterase, hAPT1 appears to be dimeric, although the mutual disposition of molecules in the two dimers differs. Unlike carboxylesterase, the substrate binding pocket and the active site of hAPT1 are occluded by the dimer interface, suggesting that the enzyme must dissociate upon interaction with substrate.
Devedjiev
Y
Y
Department of Molecular Physiology and Biological Physics, University of Virginia Health Sciences System Charlottesville, VA 22908, USA.
Dauter
Z
Z
Kuznetsov
S R
SR
Jones
T L
TL
Derewenda
Z S
ZS
D000215:Acylation; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry; D001665:Binding Sites; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D019281:Dimerization; D019143:Evolution, Molecular; D020962:Heterotrimeric GTP-Binding Proteins / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D006867:Hydrolases / Q000145:classification; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019308:Palmitic Acid / Q000378:metabolism; D011487:Protein Conformation; D011499:Protein Processing, Post-Translational; D011993:Recombinant Fusion Proteins / Q000737:chemistry; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D013329:Structure-Activity Relationship; D013869:Thiolester Hydrolases / Q000737:chemistry* / Q000145:classification
D001426:Bacterial Proteins; D011993:Recombinant Fusion Proteins; D019308:Palmitic Acid; D006867:Hydrolases; C402226:LYPLA1 protein, human; D013869:Thiolester Hydrolases; D020962:Heterotrimeric GTP-Binding Proteins