R6 HUMAN INSULIN HEXAMER (SYMMETRIC), NMR, REFINED AVERAGE STRUCTURE
[INS_HUMAN] Defects in INS are the cause of familial hyperproinsulinemia (FHPRI) [MIM:176730].    Defects in INS are a cause of diabetes mellitus insulin-dependent type 2 (IDDM2) [MIM:125852]. IDDM2 is a multifactorial disorder of glucose homeostasis that is characterized by susceptibility to ketoacidosis in the absence of insulin therapy. Clinical fetaures are polydipsia, polyphagia and polyuria which result from hyperglycemia-induced osmotic diuresis and secondary thirst. These derangements result in long-term complications that affect the eyes, kidneys, nerves, and blood vessels. Defects in INS are a cause of diabetes mellitus permanent neonatal (PNDM) [MIM:606176]. PNDM is a rare form of diabetes distinct from childhood-onset autoimmune diabetes mellitus type 1. It is characterized by insulin-requiring hyperglycemia that is diagnosed within the first months of life. Permanent neonatal diabetes requires lifelong therapy.  Defects in INS are a cause of maturity-onset diabetes of the young type 10 (MODY10) [MIM:613370]. MODY10 is a form of diabetes that is characterized by an autosomal dominant mode of inheritance, onset in childhood or early adulthood (usually before 25 years of age), a primary defect in insulin secretion and frequent insulin-independence at the beginning of the disease.  
[INS_HUMAN] Insulin decreases blood glucose concentration. It increases cell permeability to monosaccharides, amino acids and fatty acids. It accelerates glycolysis, the pentose phosphate cycle, and glycogen synthesis in liver.
Publication Abstract from PubMed
Crystallographic and NMR studies of insulin have revealed a highly flexible molecule with a range of different aggregation and structural states; the importance of these states for the function of the hormone is still unclear. To address this question, we have studied the solution structure of the insulin R6 symmetric hexamer using NMR spectroscopy. Structure determination of symmetric oligomers by NMR is complicated due to 'symmetry ambiguity' between intra- and intermonomer NOEs, and between different classes of intermonomer NOEs. Hence, to date, only two symmetric tetramers and one symmetric pentamer (VTB, B subunit of verotoxin) have been solved by NMR: there has been no other symmetric hexamer or higher-order oligomer. Recently, we reported a solution structure for R6 insulin hexamer. However, in that study, a crystal structure was used as a reference to resolve ambiguities caused by the threefold symmetry; the same method was used in solving VTB. Here, we have successfully recalculated R6 insulin using the symmetry-ADR method, a computational strategy in which ambiguities are resolved using the NMR data alone. Thus the obtained structure is a refinement of the previous R6 solution structure. Correlated motions in the final structural ensemble were analysed using a recently developed principal component method; this suggests the presence of two major conformational substates. The study demonstrates that the solution structure of higher-order symmetric oligomers can be determined unambiguously from NMR data alone, using the symmetry-ADR method. This success bodes well for future NMR studies of higher-order symmetric oligomers. The correlated motions observed in the structural ensemble suggest a new insight into the mechanism of phenol exchange and the T6 <--> R6 transition of insulin in solution.
Unraveling the symmetry ambiguity in a hexamer: calculation of the R6 human insulin structure.,O'Donoghue SI, Chang X, Abseher R, Nilges M, Led JJ J Biomol NMR. 2000 Feb;16(2):93-108. PMID:10723989
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.