Interacting polymer-modification enzymes in heparan sulfate biosynthesis

• Glucuronyl 5-epimerase (Hsepi) converts D-glucuronic acid (GlcA) into L-iduronic acid (IdoA) units, through a mechanism involving reversible abstraction of a proton at C5 of hexuronic acid residues. Incubations of a [4GlcA beta 1-4GlcNSO3 alpha 1-]n precursor substrate with recombinant enzymes in a D2O/H2O medium enabled an isotope exchange approach to the assessment of functional interactions of Hsepi with hexuronyl 2-O-sulfotrans-ferase (Hs2st) and glucosaminyl 6-O-sulfotransferase (Hs6st), both involved in the final polymer-modification steps. Enzyme complexes were supported by computational modeling and homogeneous time resolved fluores-cence. GlcA and IdoA D/H ratios related to product composition revealed kinetic isotope effects that were interpreted in terms of efficiency of the coupled epimerase and sulfotransferase reactions. Evidence for a func-tional Hsepi/Hs6st complex was provided by selective incorporation of D atoms into GlcA units adjacent to 6-O -sulfated glucosamine residues. The inability to achieve simultaneous 2-O-and 6-O-sulfation in vitro supported topologically separated reactions in the cell. These findings provide novel insight into the roles of enzyme in-teractions in heparan sulfate biosynthesis.

Subject headings

NATURVETENSKAP  -- Biologi -- Biokemi och molekylärbiologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Biochemistry and Molecular Biology (hsv//eng)

MEDICIN OCH HÄLSOVETENSKAP  -- Medicinsk bioteknologi -- Medicinsk bioteknologi (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Medical Biotechnology -- Medical Biotechnology (hsv//eng)

Keyword

Heparan sulfate

Glucuronosyl C5-epimerase

2-O-sulfotransferase

6-Osulfotransferase

Publication and Content Type

ref (subject category)

art (subject category)