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Functional analysis of human S-adenosylhomocysteine hydrolase isoforms SAHH-2 and SAHH-3

Ksenija Fumić1, Robert Beluzić, Mario Cuk

  • 1Clinical Institute of Laboratory Diagnosis, University Hospital Center, Zagreb, Croatia.

European Journal of Human Genetics : EJHG
|December 14, 2006
PubMed

Insights

Genetic variations in S-adenosylhomocysteine hydrolase (AdoHcyase) impact its thermal stability, potentially serving as risk markers for diseases linked to irregular AdoHcyase metabolism and hyperhomocysteinemia.

Area of Science:

  • Biochemistry
  • Genetics
  • Molecular Biology

Background:

  • S-adenosylhomocysteine hydrolase (AdoHcyase) regulates homocysteine levels, and elevated levels are linked to cardiovascular diseases and hyperhomocysteinemia.
  • Polymorphic isoforms of AdoHcyase (SAHH-1 to 4) exist, with SAHH-2 and SAHH-3 identified genetically.
  • SAHH-2 involves a known polymorphism (R38W) in exon 2, while SAHH-3 is associated with a novel polymorphism (G123R) in exon 3.

Purpose of the Study:

  • To investigate the molecular and catalytic effects of AdoHcyase polymorphisms (R38W and G123R) on enzyme properties.
  • To compare the characteristics of recombinant wild-type AdoHcyase with its polymorphic variants.

Main Methods:

  • Recombinant wild-type and polymorphic (R38W, G123R) AdoHcyase enzymes were produced for comparative analysis.
  • Enzyme kinetics were assessed to determine catalytic rates.
  • Circular dichroism spectroscopy was employed to evaluate thermal stability and unfolding temperatures.

Main Results:

  • Amino acid substitutions in the polymorphic variants did not significantly alter catalytic rates.
  • Circular dichroism analysis revealed reduced thermal stability in both R38W (approx. 2.6°C decrease) and G123R (approx. 1.5°C decrease) variants compared to wild-type.
  • Polymorphic proteins exhibited slightly decreased enzymatic activity (≤6%).

Conclusions:

  • AdoHcyase polymorphisms R38W and G123R affect protein thermal stability in vitro.
  • The observed alterations in thermal stability and minor decreases in enzymatic activity suggest these AdoHcyase isoforms may serve as risk markers.
  • These markers are relevant for conditions associated with irregular AdoHcyase metabolism and hyperhomocysteinemia.

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