title: Functional analysis of human S-adenosylhomocysteine hydrolase isoforms SAHH-2 and SAHH-3.
abstract: S-adenosylhomocysteine hydrolase (AdoHcyase) catalyzes the hydrolysis of AdoHcy to adenosine and homocysteine. Increased levels of AdoHcy may play a role in the development of cardiovascular diseases and numerous other conditions associated with hyperhomocysteinemia. Several polymorphic isoforms named SAHH-1 to 4 may be resolved by horizontal starch gel electrophoresis from red blood cells. We have identified the genetic background of isoforms SAHH-2 and SAHH-3. SAHH-2 represents the previously described polymorphism in exon 2 of the AdoHcyase gene (112 C>T; p.R38W). Isoform SAHH-3 is based on a new polymorphism in exon 3 (377 G>A), leading to the conversion of glycine to arginine at amino-acid position 123. To shed light on the effects of these polymorphisms on the molecular and catalytic properties of AdoHcyase, we made recombinant wild-type and polymorphic R38W and G123R enzymes for a comparative analysis. The amino-acid exchanges did not bring about major changes to the catalytic rates of the recombinant proteins. However, circular dichroism analysis showed that both polymorphisms effect the thermal stability of the recombinant protein in vitro, reducing the unfolding temperature by approximately 2.6 degrees C (R38W) and 1.5 degrees C (G123R) compared to wild-type protein. In view of the altered thermal stability, and slightly decreased enzymatic activity of polymorphic proteins (< or =6%), one may consider the analyzed AdoHcyase isoforms as risk markers for diseases caused by irregular AdoHcyase metabolism.
authors.affiliation: Clinical Institute of Laboratory Diagnosis, University Hospital Center, Zagreb, Croatia.
authors.forename: Ksenija
authors.initials: K
authors.lastname: Fumić
authors.forename: Robert
authors.initials: R
authors.lastname: Beluzić
authors.forename: Mario
authors.initials: M
authors.lastname: Cuk
authors.forename: Tea
authors.initials: T
authors.lastname: Pavkov
authors.forename: Doris
authors.initials: D
authors.lastname: Kloor
authors.forename: Ivo
authors.initials: I
authors.lastname: Barić
authors.forename: Ivana
authors.initials: I
authors.lastname: Mijić
authors.forename: Oliver
authors.initials: O
authors.lastname: Vugrek
mesh_terms: D043383:Adenosylhomocysteinase / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D019943:Amino Acid Substitution; D002942:Circular Dichroism; D004795:Enzyme Stability / Q000235:genetics; D006358:Hot Temperature; D006801:Humans; D007527:Isoenzymes / Q000235:genetics
chemical_list: D007527:Isoenzymes; D043383:Adenosylhomocysteinase