AbstractCis-nonPro peptides, a very rare feature in protein structures, are of considerable importance for two opposite reasons. On one hand, their genuine occurrences are mostly found at sites critical to biological function, from the active sites of carbohydrate enzymes to rare adjacent-residue disulfide bonds. On the other hand, a cis-nonPro can easily be misfit into weak or ambiguous electron density, which has led to a high incidence of unjustified cis-nonPro over the last decade. This paper uses the greatly expanded crystallographic data and newly stringent quality-filtering to identify the genuine occurrences and survey both individual examples and broad patterns of their functionality. The accompanying paper describes the problem of cis-nonPro over-use, including its causes, validation, and correction.We explain the procedure developed to identify genuine cis-nonPro examples with almost no false positives, including the new observation that peptides with a glycine on one side or the other need extra care to avoid mis-assignment as cis-nonPro. We then survey a sample of the varied functional roles and structural contexts of cis-nonPro, emphasizing aspects not previously covered systematically: the preferred occurrence at β-strand ends in TIM barrel structures, the concentration of occurrence in proteins that process, bind, or contain carbohydrates, and the resulting complications in defining a simple occurrence frequency.
Comparative Genomic Analysis of Limosilactobacillus Pontis Reveals Genetic Characteristics of High GC Content and Potential Niches Adaptations
