The effect of pH on the glucose response of the glucose-galactose binding protein L255C labeled with Acrylodan

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• 作者：Mayyada M.H. El-Sayed¹ ; ² ; ^{mayyada@aucegypt.edu" class="auth_mail" title="E-mail the corresponding author} ; Sheniqua R. Brown¹ ; ^{sbrown12@umbc.edu" class="auth_mail" title="E-mail the corresponding author} ; KarunaSri Mupparapu ^{karunam@umbc.edu" class="auth_mail" title="E-mail the corresponding author} ; Leah Tolosa ; ^{leah@umbc.edu" class="auth_mail" title="E-mail the corresponding author}
• 关键词：Glucose-binding protein ; pH effect ; Fluorescence ; Dissociation constant ; Lifetime measurements ; Biosensor
• 刊名：International Journal of Biological Macromolecules
• 出版年：2016
• 出版时间：May 2016
• 年：2016
• 卷：86
• 期：Complete
• 页码：282-287
• 全文大小：878 K

文摘

The glucose–galactose binding protein (GGBP) is used as an optical biosensor in medical and bioprocess applications. This paper investigates the effect of pH on the behavior of GGBP-L255C labeled with Acrylodan for the purpose of finding the optimum conditions for sensing purposes as well as for protein preparation, purification and storage. The Acrylodan–GGBP fluorescence response in absence and presence of glucose was measured under varying buffer and pH conditions. Dissociation constants (K_d) and Gibbs free energies (ΔG) for the protein-glucose binding were calculated. Binding was found to be energetically favored at slightly acidic to neutral conditions, specifically close to the pI of GBP (∼5.0). Minimal fluorescence response to glucose was exhibited at pH 3.0 accompanied by a blue shift in the steady state fluorescence spectrum. In contrast, an almost 45% response to glucose was shown at pH 4.5–9.0 with a 13-nm red shift. Frequency domain lifetime measurements and quenching with KI suggest that at highly acidic conditions both the glucose-free and the glucose-bound protein are in a conformation distinct from those observed at higher pH values.