Structure Of Insulin Molecule Research Articles

Insulin analogues for insulin receptor studies and medical applications

The structure of insulin molecule was determined by Dorothy Hodgkin in 1969. Subsequently, it has been established that insulin must rearrange upon binding to its receptor (Insulin Receptor – IR). However, all known structures of the hormone depict its storage or inactive form. It has been shown that some residues, key for IR binding, are buried inside the insulin molecule and must be exposed for an efficient insulin-IR complex formation. It has been postulated that the C-terminal region of the B-chain (~B20-B30) is dynamic in this process, and that the detachment of the B20-B30 β-strand leads to the activation of insulin. However, the understanding of the molecular basis of the insulin regulatory role is hindered by the lack of the structure of the insulin-IR complex; only 3-D description of the apo-form of the IR ectodomain is known. The very complex molecular biology behind expression and production of IR fragments also hampers progress in this field. In order to facilitate progress towards determination of the insulin-IR complex crystal structure this work delivered: (i) structural characterisation of highly-active insulin analogues for stable hormone-IR complexes, (ii) development of various attempts for an alternative production of L1 domain of human IR, (iii) structural characterisation of the role of residues B24 and B26 for insulin function, (iv) clarification of individual contributions of hydrogen bonds stabilising the insulin dimer, (v) understanding of the structural basis of different functionality of click-chemistry based novel insulin analogues. This work established that: (i) the structural signature of the highly active insulin analogues is new -turn at the Cterminus of the B-chain (the B26 turn) achieved by trans-to-cis isomerisation of the PheB25- TyrB26 peptide bond. This conformational change exposes residues responsible for IR binding, (ii) the production of the L1 domain in E. coli, instead of the usual mammalian expression system, is not feasible, (iii) the structural invariance of the PheB24 is fundamental to the formation of the insulin-IR complex. It acts as an anchoring and side-chain pivot for the B26 turn, (iv) removal of the NHB25-COA19 dimer interface hydrogen bond is sufficient for a complete disruption of the dimer, whilst the other four hydrogen bonds had a less marked effect in this process, (v) the formation of the B26 turn can be efficiently mimicked by click-chemistry based intra-B-chain crosslinks. These results provide a wealth of information about the active form of insulin, they provide important tools towards the first insulin-IR complex, and deliver novel insulin analogues.

Interaction of dipalmitoyl phosphatidylcholine (DPPC) liposomes and insulin

Insulin, a peptide that has been used for decades in the treatment of diabetes, has well-defined properties and delivery requirements. Liposomes, which are lipid bilayer vesicles, have gained increasing attention as drug carriers which reduce the toxicity and increase the pharmacological activity of various drugs. The molecular interaction between (uncharged lipid) dipalmitoyl phosphatidylcholine (DPPC) liposomes and insulin has been characterized by using Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction. The characteristic protein absorption band peaks, Amide I (at about 1660 cm−1) and Amide II band (at about 1546 cm−1) are potentially reduced in the liposome insulin complex. Wide-angle x-ray scattering measurements showed that the association of insulin with DPPC lipid of liposomes still maintains the characteristic DPPC diffraction peaks with almost no change in relative intensities or change in peak positions. The absence of any shift in protein peak positions after insulin being associated with DPPC liposomes indicates that insulin is successfully forming complex with DPPC liposomes with possibly no pronounced alterations in the structure of insulin molecule.