<p>The alpha/beta hydrolase fold [<cite idref="PUB00004958"/>] is common to a number of hydrolytic enzymes of widely differing phylogenetic origin and catalytic function. The core of each enzyme is an alpha/beta-sheet (rather than a barrel), containing 8 strands connected by helices [<cite idref="PUB00004958"/>]. The enzymes are believed to have diverged from a common ancestor, preserving the arrangement of the catalytic residues. All have a catalytic triad, the elements of which are borne on loops, which are the best conserved structural features of the fold. Esterase (EST) from <taxon tax_id="303">Pseudomonas putida</taxon> is a member of the alpha/beta hydrolase fold superfamily of enzymes [<cite idref="PUB00038968"/>].</p><p>In most of the family members the beta-strands are parallels, but some have an inversion of the first strands, which gives it an antiparallel orientation. The catalytic triad residues are presented on loops. One of these is the nucleophile elbow and is the most conserved feature of the fold. Some other members lack one or all of the catalytic residues. Some members are therefore inactive but others are involved in surface recognition. The ESTHER database [<cite idref="PUB00043472"/>] gathers and annotates all the published information related to gene and protein sequences of this superfamily [<cite idref="PUB00043472"/>].</p><p>This entry represents fold-1 of alpha/beta hydrolase.</p>