TY - JOUR
T1 - Tryptophan Fluorescence Yields and Lifetimes as a Probe of Conformational Changes in Human Glucokinase
AU - Zelent, Bogumil
AU - Bialas, Chris
AU - Gryczynski, Ignacy
AU - Chen, Pan
AU - Chib, Rahul
AU - Lewerissa, Karina
AU - Corradini, Maria G.
AU - Ludescher, Richard D.
AU - Vanderkooi, Jane M.
AU - Matschinsky, Franz M.
N1 - Funding Information:
The work was supported by grants from NIDDK no. 22122 and 19,525 (F.M.M.), NSF grant CBET-1264608 (I.G.) and National Research Initiative or Agriculture and Food Research Initiative Grant no. 2014–67,017-2149 (R.D.L., B.Z.& M.G.C.) from USDA National Institute of Food and Agriculture, Improving Food Quality.
Publisher Copyright:
© 2017, Springer Science+Business Media New York.
PY - 2017/9/1
Y1 - 2017/9/1
N2 - Five variants of glucokinase (ATP-D-hexose-6-phosphotransferase, EC 2.7.1.1) including wild type and single Trp mutants with the Trp residue at positions 65, 99, 167 and 257 were prepared. The fluorescence of Trp in all locations studied showed intensity changes when glucose bound, indicating that conformational change occurs globally over the entire protein. While the fluorescence quantum yield changes upon glucose binding, the enzyme’s absorption spectra, emission spectra and fluorescence lifetimes change very little. These results are consistent with the existence of a dark complex for excited state Trp. Addition of glycerol, L-glucose, sucrose, or trehalose increases the binding affinity of glucose to the enzyme and increases fluorescence intensity. The effect of these osmolytes is thought to shift the protein conformation to a condensed, high affinity form. Based upon these results, we consider the nature of quenching of the Trp excited state. Amide groups are known to quench indole fluorescence and amides of the polypeptide chain make interact with excited state Trp in the relatively unstructured, glucose-free enzyme. Also, removal of water around the aromatic ring by addition of glucose substrate or osmolyte may reduce the quenching.
AB - Five variants of glucokinase (ATP-D-hexose-6-phosphotransferase, EC 2.7.1.1) including wild type and single Trp mutants with the Trp residue at positions 65, 99, 167 and 257 were prepared. The fluorescence of Trp in all locations studied showed intensity changes when glucose bound, indicating that conformational change occurs globally over the entire protein. While the fluorescence quantum yield changes upon glucose binding, the enzyme’s absorption spectra, emission spectra and fluorescence lifetimes change very little. These results are consistent with the existence of a dark complex for excited state Trp. Addition of glycerol, L-glucose, sucrose, or trehalose increases the binding affinity of glucose to the enzyme and increases fluorescence intensity. The effect of these osmolytes is thought to shift the protein conformation to a condensed, high affinity form. Based upon these results, we consider the nature of quenching of the Trp excited state. Amide groups are known to quench indole fluorescence and amides of the polypeptide chain make interact with excited state Trp in the relatively unstructured, glucose-free enzyme. Also, removal of water around the aromatic ring by addition of glucose substrate or osmolyte may reduce the quenching.
KW - Aromatic groups
KW - Dark complexes
KW - Glucokinase
KW - Glucose
KW - Glycerol
KW - Osmolites
KW - Tryptophan fluorescence
UR - http://www.scopus.com/inward/record.url?scp=85018810098&partnerID=8YFLogxK
U2 - 10.1007/s10895-017-2099-x
DO - 10.1007/s10895-017-2099-x
M3 - Article
C2 - 28432632
AN - SCOPUS:85018810098
SN - 1053-0509
VL - 27
SP - 1621
EP - 1631
JO - Journal of Fluorescence
JF - Journal of Fluorescence
IS - 5
ER -