Multinuclear NMR resonance assignments and the secondary structure of Escherichia coli thioesterase/protease I: a member of a new subclass of lipolytic enzymes.
Escherichia coli thioesterase/protease I is a 183 amino acid protein with a molecular mass of 20,500. This protein belongs to a new subclass of lipolytic enzymes of the serine protease superfamily, but with a new GDSLS consensus motif, of which no structure has yet been determined. The protein forms a tetramer at pH values above 6.5 and exists as a monomer at lower pH values. Both monomer and tetramer are catalytically active. From analysis of a set of heteronuclear multidimensional NMR spectra with uniform and specific amino acid labeled protein samples, we have obtained near-complete resonance assignments of the backbone 1H, 13C and 15N nuclei (BMRB databank accession number 4060). The secondary structure of E. coli thioesterase/protease I was further deduced from the consensus chemical shift indices, backbone short- and medium-range NOEs, and amide proton exchange rates. The protein was found to consist of four beta-strands and seven alpha-helices, arranged in alternate order. The four beta-strands were shown to form a parallel beta-sheet. The topological arrangement of the beta-strands of -1x, +2x, +1x appears to resemble that of the core region of the alpha beta hydrolase superfamily, typically found in common lipases and esterases. However, substantial differences, such as the number of beta-strands and the location of the catalytic triad residues, make it difficult to give a definitive classification of the structure of E. coli thioesterase/protease I at present.
Division of Structural Biology, Institute of Biomedical Sciences, Republic of China.
T H
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Lin
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Chen
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Huang
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Lee
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Shaw
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Huang
D000595:Amino Acid Sequence; D002247:Carbon Isotopes; D004926:Escherichia coli; D007553:Isotope Labeling; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000737:chemistry; D009587:Nitrogen Isotopes; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods*; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D012697:Serine Endopeptidases / Q000737:chemistry*; D013869:Thiolester Hydrolases / Q000737:chemistry*
D002247:Carbon Isotopes; D009097:Multienzyme Complexes; D009587:Nitrogen Isotopes; D013869:Thiolester Hydrolases; C025097:Escherichia coli periplasmic proteinase; D012697:Serine Endopeptidases