Background: A new type of domain structure, an all parallel beta class, has recently been observed in two pectate lyases, PelC and PelE. The atomic models have been analyzed to determine whether the new tertiary fold exhibits unusual structural features.
Results: The polypeptide backbone exhibits no new types of secondary structural elements. However, novel features occur in the amino acid side chain interactions. The side chain atoms form linear stacks that include asparagine ladders, serine stacks, aliphatic stacks, and ringed-residue stacks. A new type of beta-sandwich between parallel beta-sheets is observed with properties that are more characteristic of antiparallel beta-sheets.
Conclusion: An analysis of the PelC and PelE structures, belonging to an all parallel beta structural class, reveals novel amino acid side chain interactions, a new type of beta-sandwich and an atypical amino acid composition of parallel beta-sheets. The findings are relevant to three-dimensional structural predictions.