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Abstract
Enzymatic removal of blood group A and B antigens from the surface of red blood cells to develop universal blood was a pioneering vision originally proposed more than 25 years ago. A great variety of enzymes, potentially suitable for enzymatic conversion of red blood cells, has been described since, but the process has not been economically viable because of the poor kinetic properties and low pH optimum of enzymes. Recently, the identification of two new families of bacterial glycosidases with enhanced kinetic properties for the removal of A and B antigens at neutral pH marked a milestone in the field of transfusion medicine (Citation). Here we present a detailed structural analysis of Elizabethkingia meningosepticum a-N-acetylgalactosaminidase (NagA) shown to efficiently cleave the A antigen. NagA, a member of glycoside hydrolase (GH) family 109, employs an unusual catalytic mechanism involving NAD+. Comparison of the active-center structure with that of members of GH family 4 reveals a striking degree of structural similarity that allows the postulation of a common reaction mechanism and illustrates a beautiful example of convergent evolution.
Acknowledgements
E.P.B., S.B.L. and H.C. are funded by the Center of Excellence Program of the University of Copenhagen, the Benzon Foundation and the Carlsberg Foundation. We are grateful to the beamline staff of the European Synchrotron Research Facility (Grenoble, France) for assistance with data collection. GP is supported by a doctoral fellowship from the French Ministry of Research and the Délégation Générale pour l’Armement (administered by Jean-Jacques Lataillade).
Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.