Characterization of left‐handed beta helix‐domains, and identification and functional annotation of proteins containing such domains

Only about 0.3% of the entries in UniProt database have manually curated annotation. Annotation at the molecular level often relies on low‐throughput one‐protein‐at‐a‐time approach. Computational methods bridge this gap by assigning function based on sequence and/or fold similarity. Left‐handed beta helix (LbH) consists of three repeating six‐stranded beta‐strands forming an 18‐mer turn of the helix. Analysis of LbH‐domains showed that variations are found in the number of residues in a beta‐strand (5‐7, 6 being the most common), number of turns (4–10) of the helix, insertions of one or more loops of variable length (0‐36 residues), and the location of loop insertion. An 18‐mer HMM profile was created which identifies LbH‐domain containing proteins using sequence as the only input; the number of false positives is zero when proteins tested were those with known 3D structures. 136 474 entries of TrEMBL database were found to contain LbH‐domain. Rules developed by analyzing LbH‐domain containing acyltransferases, gamma‐class carbonic anhydrases, and nucleotidyltransferases have led to the annotation of 17 389 TrEMBL entries which currently have no functional tag.