Shoemaker Glen K, Soya Naoto, Palcic Monica M, Klassen John S
Department of Chemistry, University of Alberta, Edmonton, Alberta, T6G 2G2, Canada.
Glycobiology. 2008 Aug;18(8):587-92. doi: 10.1093/glycob/cwn043. Epub 2008 May 28.
Affinities of the human blood group glycosyltransferases, alpha-(1-->3)-N-acetylgalactosaminyltransferase (GTA) and alpha-(1-->3)-galactosyltransferase (GTB) for their common acceptor substrate alpha-l-Fucp-(1-->2)-beta-d-Galp-O(CH2)(7)CH3 (1), in the absence and presence of bound uridine 5'-diphosphate (UDP) and Mn2+ were determined using temperature-controlled electrospray ionization mass spectrometry. The presence of bound UDP and Mn(2+) in the donor binding site has a marked influence on the thermodynamic parameters for the association of 1 with GTA and GTB. Both the enthalpy and entropy of association (DeltaH(a), DeltaS(a)) decrease significantly. However, the free energy of association (DeltaG(a)) is unchanged at physiological temperature. The differences in the DeltaH(a) and DeltaS(a) values determined in the presence and absence of bound UDP are attributed to structural changes in the glycosyltransferases induced by the simultaneous binding of 1 and UDP.
在存在和不存在结合的尿苷5'-二磷酸（UDP）及锰离子（Mn2+）的情况下，利用温控电喷雾电离质谱法测定了人类血型糖基转移酶α-(1→3)-N-乙酰半乳糖胺基转移酶（GTA）和α-(1→3)-半乳糖基转移酶（GTB）对其共同受体底物α-L-岩藻糖基-(1→2)-β-D-半乳糖基-O(CH2)(7)CH3（1）的亲和力。供体结合位点中结合的UDP和Mn(2+)的存在，对1与GTA和GTB结合的热力学参数有显著影响。结合的焓和熵（ΔH(a)，ΔS(a)）均显著降低。然而，在生理温度下结合自由能（ΔG(a)）不变。存在和不存在结合的UDP时所测定的ΔH(a)和ΔS(a)值的差异，归因于1和UDP同时结合所诱导的糖基转移酶结构变化。
