Data were collected on two separate protein systems in March 96 at Station A1; S-adenosine homocysteine hydrolase and d II crystallin. S-adenosine homocysteine hydrolase: The enzyme transfer of a methyl group from S-adenosylmethionine (AdoMet) to an acceptor molecule, i.e. biological transmethylation, is a ubiquitous set of reactions involved in regulating a diverse array of physiologically important processes. The activities of all AdoMet-dependent methyltransferases are regulated by the intracellular level of S-adenosyl-L-homocysteine (AdoHcy), a product inhibitor of AdoMet-dependent transmethylations. Since in all eukaryotic cells, the intracellular level of AdoHcy is regulated by S-adenosylhomocysteine hydrolase (SAH), this enzyme is an attractive target for drug design. Inhibitors of this enzyme have already been shown to exhibit antiviral (e.g. cytomegalovirus, respiratory syncytical virus and rabies), antiparasitic (e.g. Leishmania, leishmaniasis; Plasmodium, malaria; Trypanosoma, African sleeping sickness) as well as anti-arthritic and immunosuppressive properties. High resolution native data and several putative heavy atom derivative data sets were collected. The native data diffracted to ~2.10_ resolution (>50% of data in final shell 2.15-2.10_ had an I/s(I)>2) with an overall merging R value of 0.68 (~4-fold redundancy). The data processing and analysis of the heavy atom derivative data sets and structure determination of the protein is in progress. Delta II crystallin Argininosuccinate lyase(ASL) catalyzes the reversible breakdown of argininosuccinate to arginine and fumarate, a reaction which is involved in the biosynthesis of arginine in all organisms and in the urea cycle in ureotelic species. In humans, mutations in ASL result in the argininosuccinic aciduria, the second most common urea cycle disorder. Although ASL's primary physiological role is in the liver, it is also found in all mammalian tissues where with argininosuccinate synthetase it forms a truncated urea cycle. The significance of this abbreviated urea cycle has only recently been realized with the discovery that arginine-derived nitric oxide, the key cell signaling molecule, is responsible for the hypotension in septic and cytokine-induced circulatory shock. The enzymes, argininosuccinate synthetase, argininosuccinate lyase and nitric oxide synthetase constitute the arginine-citrulline cycle. Since existing crystals of recombinant human ASL only diffract to 4.0 _ resolution, we have exploited the amino acid sequence similarities and ASL activity exhibited by the eye lens protein, d II crystallin, as a means of determining the mechanism of the reaction catalyzed by both proteins. Due to a combination of crystal quality and loss of data collection time we were unsuccessful in measuring complete native dataset of the wild-type duck dII crystallin protein.
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