A team at the University of British Columbia, under Steve Withers, has demonstrated for the first time the use of a designer enzyme to remove a significant amount of antigen-determining sugars from red blood cells.
A human red blood cell can have either A or B antigens, both at the same time, or none of the two on its surface, resulting in the grouping of blood types into A, B, AB, and O respectively. The absence of either the A or B antigen from one’s blood also corresponds to the presence of anti-B or anti-A antibodies in one’s blood plasma that can interact with the corresponding blood types in a potentially-fatal immune reaction, creating restrictions on the blood types that can be used for transfusions.
As such, researchers have long pursued a means to remove antigens from red blood cells so that all donated blood can be converted to be universally acceptable. Withers’ team’s work involved the upgrading of endo-beta-galactosidase Sp3GH98, an enzyme previously determined to be able to break one type of the linkages (Type 2) that bind the antigenic sugars to the surfaces of red blood cells but not some of the other more enzyme-resistant types.
They used a technique known as directed evolution. This is a trial-and-error method that makes mutant enzymes with variations in the active site used to break the antigen-surface linkages, and subsequently tested these mutants for their linkage-breaking effectiveness. Multiple iterations of this process led to the identification of a mutant design that is able to break Type 1 enzyme-resistant linkages 170-times more effectively than the original Sp3GH98.
The team will subsequently be looking at designing enzymes to break Type 3 and Type 4 linkages, the remaining two resistant types of linkage to achieve the creation of fully non-antigenic blood. The problem of non-antigenic blood being more prone to removal by the body’s own metabolism will also need to be overcome before this technology can be used in medical applications.
Read the original paper at DOI: 10.1021/ja5116088