3S2Z: Crystal Structure Of The Lactobacillus Johnsonii Cinnamoyl Esterase Lj0536 S106a Mutant In Complex With Caffeic Acid

Citation:
Abstract
BACKGROUND: Microbial enzymes produced in the gastrointestinal tract are primarily responsible for the release and biochemical transformation of absorbable bioactive monophenols. In the present work we described the crystal structure of LJ0536, a serine cinnamoyl esterase produced by the probiotic bacterium Lactobacillus johnsonii N6.2. METHODOLOGY/PRINCIPAL FINDINGS: We crystallized LJ0536 in the apo form and in three substrate-bound complexes. The structure showed a canonical alpha/beta fold characteristic of esterases, and the enzyme is dimeric. Two classical serine esterase motifs (GlyXSerXGly) can be recognized from the amino acid sequence, and the structure revealed that the catalytic triad of the enzyme is formed by Ser(106), His(225), and Asp(197), while the other motif is non-functional. In all substrate-bound complexes, the aromatic acyl group of the ester compound was bound in the deepest part of the catalytic pocket. The binding pocket also contained an unoccupied area that could accommodate larger ligands. The structure revealed a prominent inserted alpha/beta subdomain of 54 amino acids, from which multiple contacts to the aromatic acyl groups of the substrates are made. Inserts of this size are seen in other esterases, but the secondary structure topology of this subdomain of LJ0536 is unique to this enzyme and its closest homolog (Est1E) in the Protein Databank. CONCLUSIONS: The binding mechanism characterized (involving the inserted alpha/beta subdomain) clearly differentiates LJ0536 from enzymes with similar activity of a fungal origin. The structural features herein described together with the activity profile of LJ0536 suggest that this enzyme should be clustered in a new group of bacterial cinnamoyl esterases.
PDB ID: 3S2ZDownload
MMDB ID: 93324
PDB Deposition Date: 2011/5/17
Updated in MMDB: 2012/10
Experimental Method:
x-ray diffraction
Resolution: 1.76  Å
Source Organism:
Similar Structures:
Biological Unit for 3S2Z: dimeric; determined by author and by software (PISA)
Molecular Components in 3S2Z
Label Count Molecule
Proteins (2 molecules)
2
Cinnamoyl Esterase
Molecule annotation
Chemicals (18 molecules)
1
16
2
2
* Click molecule labels to explore molecular sequence information.

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