One origin for metallo-β-lactamase activity, or two? An investigation assessing a diverse set of reconstructed ancestral sequences based on a sample of phylogenetic trees

• Published in: Journal of molecular evolution Vol. 79; no. 3-4; pp. 117 - 129
• Main Authors: Alderson, Rosanna G., Barker, Daniel, Mitchell, John B. O.
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.10.2014
• Subjects: Amino Acid Sequence; Animal Genetics and Genomics; Bacteria - genetics; Bacterial Proteins - genetics; beta-Lactamases - genetics; Biological Evolution; Biomedical and Life Sciences; Cell Biology; Evolutionary Biology; Life Sciences; Likelihood Functions; Microbiology; Models, Genetic; Models, Molecular; Molecular Sequence Data; Original; Original Article; Phylogeny; Plant Genetics and Genomics; Plant Sciences; Protein Structure, Tertiary; Sequence Homology, Amino Acid; Phylogenetics; Metallo-β-lactamase; Exaptation; Most recent common ancestor; Ancestral sequence reconstruction; Antibiotic resistance
• ISSN: 0022-2844; 1432-1432
• DOI: 10.1007/s00239-014-9639-7

Bacteria use metallo-β-lactamase enzymes to hydrolyse lactam rings found in many antibiotics, rendering them ineffective. Metallo-β-lactamase activity is thought to be polyphyletic, having arisen on more than one occasion within a single functionally diverse homologous superfamily. Since discovery of multiple origins of enzymatic activity conferring antibiotic resistance has broad implications for the continued clinical use of antibiotics, we test the hypothesis of polyphyly further; if lactamase function has arisen twice independently, the most recent common ancestor (MRCA) is not expected to possess lactam-hydrolysing activity. Two major problems present themselves. Firstly, even with a perfectly known phylogeny, ancestral sequence reconstruction is error prone. Secondly, the phylogeny is not known, and in fact reconstructing a single, unambiguous phylogeny for the superfamily has proven impossible. To obtain a more statistical view of the strength of evidence for or against MRCA lactamase function, we reconstructed a sample of 98 MRCAs of the metallo-β-lactamases, each based on a different tree in a bootstrap sample of reconstructed phylogenies. InterPro sequence signatures and homology modelling were then used to assess our sample of MRCAs for lactamase functionality. Only 5 % of these models conform to our criteria for metallo-β-lactamase functionality, suggesting that the ancestor was unlikely to have been a metallo-β-lactamase. On the other hand, given that ancestral proteins may have had metallo-β-lactamase functionality with variation in sequence and structural properties compared with extant enzymes, our criteria are conservative, estimating a lower bound of evidence for metallo-β-lactamase functionality but not an upper bound.