MadSci Network: Molecular Biology |
Hi Amy, Often the whole molecule is mutated- doing it this way gives the molecule more degrees of freedom to vary during the evolutionary process and thus a bigger universe of solutions to explore. If there is a sequence within the molecule that needs to be evolved (sorry about the clumsy wording) but the rest of the molecule needs to remain constant, then the evolutionary process would be restricted to the region of interest. For example, the adaptive immune system does some of the latter. The majority of the immunoglobulin molecule remains constant and can thus continue to interact normally with Fc receptors, complement etc. whereas the variable regions involved in binding the target of the antibody can vary and the "improved" versions are selected by the immune system. In the immune system, generally this evolution is directed towards increasing specificity and avidity of binding of the antibody to the target. So, to make a long answer short, both approaches are used, and the situation where a part of the molecule only is evolved depends on the application. Usually a fair bit is known about the molecule that is to be altered by evolution when an approach using just a part of that molecule is used.
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