title: The metastability of human UDP-galactose 4'-epimerase (GALE) is increased by variants associated with type III galactosemia but decreased by substrate and cofactor binding.
abstract: Type III galactosemia is an inherited disease caused by mutations which affect the activity of UDP-galactose 4'-epimerase (GALE). We evaluated the impact of four disease-associated variants (p.N34S, p.G90E, p.V94M and p.K161N) on the conformational stability and dynamics of GALE. Thermal denaturation studies showed that wild-type GALE denatures at temperatures close to physiological, and disease-associated mutations often reduce GALE's thermal stability. This denaturation is under kinetic control and results partly from dimer dissociation. The natural ligands, NAD(+) and UDP-glucose, stabilize GALE. Proteolysis studies showed that the natural ligands and disease-associated variations affect local dynamics in the N-terminal region of GALE. Proteolysis kinetics followed a two-step irreversible model in which the intact protein is cleaved at Ala38 forming a long-lived intermediate in the first step. NAD(+) reduces the rate of the first step, increasing the amount of undigested protein whereas UDP-glucose reduces the rate of the second step, increasing accumulation of the intermediate. Disease-associated variants affect these rates and the amounts of protein in each state. Our results also suggest communication between domains in GALE. We hypothesize that, in vivo, concentrations of natural ligands modulate GALE stability and that it should be possible to discover compounds which mimic the stabilising effects of the natural ligands overcoming mutation-induced destabilization.
authors.affiliation: Department of Physical Chemistry, Faculty of Sciences, University of Granada, Av. Fuentenueva s/n, 18071, Spain. Electronic address: angelpey@ugr.es.
authors.forename: Angel L
authors.initials: AL
authors.lastname: Pey
authors.affiliation: Department of Physical Chemistry, Faculty of Sciences, University of Granada, Av. Fuentenueva s/n, 18071, Spain.
authors.forename: Esperanza
authors.initials: E
authors.lastname: Padín-Gonzalez
authors.affiliation: Department of Physical Chemistry, Faculty of Sciences, University of Granada, Av. Fuentenueva s/n, 18071, Spain.
authors.forename: Noel
authors.initials: N
authors.lastname: Mesa-Torres
authors.affiliation: School of Biological Sciences, Queeńs University Belfast, Medical Biology Centre, 97 Lisburn Road, Belfast BT9 7BL, UK. Electronic address: d.timson@qub.ac.uk.
authors.forename: David J
authors.initials: DJ
authors.lastname: Timson
mesh_terms: D001407:Bacillus / Q000378:metabolism; D002151:Calorimetry; D018360:Crystallography, X-Ray; D004252:DNA Mutational Analysis; D004926:Escherichia coli / Q000378:metabolism; D005690:Galactose / Q000737:chemistry; D005693:Galactosemias / Q000201:enzymology* / Q000235:genetics*; D014644:Genetic Variation; D006801:Humans; D008024:Ligands; D009154:Mutation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D059748:Proteolysis; D013053:Spectrophotometry; D013379:Substrate Specificity; D013696:Temperature; D013820:Thermolysin / Q000737:chemistry; D014534:UDPglucose 4-Epimerase / Q000737:chemistry*; D014532:Uridine Diphosphate Glucose / Q000737:chemistry
chemical_list: D008024:Ligands; D013820:Thermolysin; D014534:UDPglucose 4-Epimerase; D014532:Uridine Diphosphate Glucose; D005690:Galactose
keywords: Ligand binding; Protein aggregation; Protein conformational stability; Protein dynamics; Proteolysis; Type III galactosemia