Substrate discrimination by the human GTP fucose pyrophosphorylase

GTP-l-fucose pyrophosphorylase (GFPP, E. C. 2.7.7.30) catalyzes the reversible condensation of guanosine triphosphate and beta-l-fucose-1-phosphate to form the nucleotide-sugar GDP-beta-l-fucose. The enzyme functions primarily in the mammalian liver and kidney to salvage free l-fucose during the breakdown of glycolipids and glycoproteins. The mechanism by which this protein discriminates between substrate and nonsubstrate molecules has been elucidated for the first time in this study. The ability of GFPP to form nucleotide-sugars from a series of base-, ribose-, phosphate-, and hexose-modified precursor molecules has revealed that the enzyme active site senses a series of substrate substituents that drive substrate/nonsubstrate discrimination. These substituents alter the ability of the precursor molecule to interact with the enzyme, as measured by either changes in the Michaelis constant, K(m), the binding affinity, K(a), or through changes in enzymatic turnover, k(cat). In this work, the combined substrate binding and enzyme analysis has revealed that the nature of the purine base is the major determinant in substrate specificity, followed by the nature of the hexose-1-P, and finally by the ribose moiety. Binding is enthalpy-driven and does not involve proton transfer. For the majority of nucleotide-sugar analogues, binding to GFPP is entropically unfavorable; however, surprisingly, a few of the substrate analogues tested bind to GFPP with a favorable entropic term.     

Expert Roundtable on Continuous Glucose Monitoring

ObjectiveThe objective of this study was to define an expert opinion on continuous glucose monitoring (CGM) in persons with type 2 diabetes mellitus, including its advantages, barriers, and best clinical practices for initiation, patient-clinician communication, and data management.MethodsA series of virtual discussions was held to recommend improvements to clinical practice and design clinical tools for primary care clinicians. Participants included endocrinologists, primary care physicians, physician assistants, advanced practice nurses, and diabetes care and education specialists.ResultsThe expert panels recommended CGM as a supplement to blood glucose monitoring and hemoglobin A1c for managing diabetes in persons with diabetes (PWDs). CGM can help predict potential pitfalls in glycemic management, including hypo and hyperglycemic excursions, which directly influence lifestyle changes, medication initiation, and dosing decisions. A toolkit was designed with practical guidance on the integration of CGM into clinical practice, interpretation of results, clinical guidelines, a patient action plan, and other useful management tools.ConclusionThis review summarizes the findings from a roundtable discussion with endocrinology and primary care clinicians, a discussion of the advantages and challenges of CGM, and clinical approaches to improving the care of PWDs. CGM offers more detailed tracking of glucose levels than blood glucose monitoring or hemoglobin A1c, and it can detect asymptomatic hypoglycemia. Specialized education of providers, the cost to patients and providers, and data management are barriers to the widespread adoption of CGM for PWDs.