Structure of human insulin cocrystallized with protamine and urea
[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
Insulin NPH (neutral protamine hagedorn) has for long been one of the most important therapeutic formulations for the treatment of diabetes. The protracted action profile of NPH formulations is gained from crystallizing insulin with zinc in the presence of the basic poly-arginine peptide protamine. In spite of its long history and successful use, the binding mode of the insulin-protamine complex is not known. In this study, three different systems were used to study protamine binding to insulin. In the first system, crystals of an insulin-protamine complex grown in the presence of urea and diffracting to 1.5A resolution were analyzed. In the second system, a shorter peptide consisting of 12 arginine residues was co-crystallized with insulin in order to reduce the flexibility and thereby improve the electron density of the peptide. Both systems yielded data to a significantly higher resolution than obtained previously. In addition, a third system was analyzed where crystals of insulin and protamine were grown in the absence of urea, with conditions closely resembling the pharmaceutical formulation. Data from these NPH microcrystals could for the first time be collected to 2.2A resolution at a micro focused X-ray beamline. Analysis of all three crystal forms reveal potential protamine density located close to the solvent channel leading to the centrally located zinc atoms in the insulin hexamer and support that protamine binds to insulin in a not well defined conformation.
Structural characterization of insulin NPH formulations.,Norrman M, Hubalek F, Schluckebier G Eur J Pharm Sci. 2007 Apr;30(5):414-23. Epub 2007 Jan 20. PMID:17339105
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.