As the quest to develop new ways of fighting cancer continues, methods such as prodrug therapy are promising but currently lack the ideal tools necessary for effective treatment. One such tool is a non-immunogenic enzyme that catalyzes the deamination of cytosine, converting it to uracil. There is clinical need for a human cytosine deaminase for use as a prodrug activator in suicide gene therapy, where a cytosine deaminase can catalyze the reaction of the cytosine derivative 5-fluorocytosine (a harmless chemical) into 5-fluorouracil (a cytotoxin). While there are cytosine deaminases that exist in nature, there is no human enzyme capable of catalyzing this reaction. The use of non-human enzymes in prodrug therapy often fails due to the immunogenicity issues that can arise. Therefore, by taking a human enzyme and altering its specificity such that it can catalyze the deamination of cytosine, these immunogenicity issues can be avoided.

The “Pack the Holes and Fight Cancer” puzzles are based on a previously designed human guanine deaminase in which its specificity was successfully changed from guanine to ammelide (which has a structure is very similar cytosine) by modification of a catalytic loop. This original re-design left a few large holes near the loop and ligand. Thus, to increase the activity of the enzyme and move closer to the final goal of creating a human cytosine deaminase, we need to pack these holes! There are two puzzles that offer different packing possibilities.

Your designs will be ranked based on score, packing, and number of additional contacts made to stabilize the loop residues 119-121 (particularly the sidechain of N120). The most promising of your designs will then be synthesized and experimentally tested in the Baker lab. We look forward to seeing all of the exciting new solutions you come up with!

( Posted by  JMDNivala 191 16658  |  Tue, 11/10/2009 - 00:33  |  0 comments )