Deposition of amyloid in pancreatic islets is a common feature in human type 2 diabetic subjects but because of its insolubility and low tissue concentrations, the structure of its monomer has not been determined. We describe a peptide, of calculated molecular mass 3905 Da, that was a major protein component of amyloid-rich pancreatic extracts of three type 2 diabetic patients. After collagenase treatment, an extract containing 20-50% amyloid was solubilized by sonication into 70% formic acid and the peptide was purified by gel filtration followed by reverse-phase high-performance liquid chromatography. We term this peptide diabetes-associated peptide, as it was not detected in extracts of pancreas from any of six normal subjects. Diabetes-associated peptide contains 37 amino acids and is 46% identical to the sequences of rat and human calcitonin gene-related peptide, indicating that these peptides are related in evolution. Sequence identities with conserved residues of the insulin A chain were also seen in a 16-residue segment. On extraction, the islet amyloid is particulate and insoluble like the core particles of Alzheimer disease. Their monomers have similar molecular masses, each having a hydropathic region that can probably form 13-pleated sheets.

The glycosylation of the circulating immunoglobulin-gamma (IgG) antibody molecules changes in rheumatoid arthritis. The extent of the changes correlates with the disease severity and reverses in remission. We demonstrate here that the alteration in glycosylation associated with rheumatoid arthritis can create a new mode for the interaction of IgG with complement through binding to the collagenous lectin mannose-binding protein (MBP). Rheumatoid arthritis is associated with a marked increases in IgG glycoforms that lack galactose (referred to as G0 glycoforms) in the Fc region of the molecule and that terminate in N-acetyl glucosamine (GlcNAc). We show, using nuclear magnetic resonance (NMR) and X-ray data, that these terminal GlcNAc residues become accessible for MBP binding. We further demonstrate that multiple presentation of IgG-G0 glycoforms to MBP results in activation of the complement. This suggests that a contribution to the chronic inflammation of the synovial membrane could arise from the localization of the IgG-G0 glycoforms in the affected joint and from resulting activation of complement.

Solution scattering experiments using both X-rays and neutrons are reported for human complement component C 3 and up to six other glycoprotein fragments that are derived from C3. The X-ray and neutron molecular masses and neutron matchpoints are in agreement with the known primary sequence of C 3. The X-ray radius of gyration RG of C3 is 5.2 nm and is similar for the related forms C~U , C3(a+ b) and C3 b. The X-ray cross-sectional radius of gyration Rxs of C3b is however less than that of C3, C3u and C3(a+b). The major fragments of C3b, namely C3c and C3dg, were studied. The Ro of C3c is 4.7 nm and for C3dg is 2.9 nm. C3c and C 3dg do not interact when they coexist in solution in equimolar amounts. When C 3u is cleaved into iC 3u, the RG of iC3u increases to 5.9 nm and its Rxs decreases, showing that C3c and C3dg behave as independent entities within the parent glycoprotein. Analyses of the neutron RG and Rxs values by contrast variation techniques confirm the X-ray analyses, and show no evidence for significant hydrophobic or hydrophilic domains within C3 or any of its fragments. Shape analyses show that C3, C3c and C3dg are elongated particles. Debye models were developed using the scattering curve out to Q = 1.6 nm-I . These show that C 3 and C 3c resemble oblate ellipsoids while C3dg resembles a prolate ellipsoid. C3dg lies on the long edge of C3c within C3. The dimensions of the modelsare 18 nmx 2 nm x 10 nmforC3,18 nmx 2 nm x 7 nmforC3cand 10 nm x 2 nm x 3 nm forC3dg. These models are compatible with analyses of the scattering curve RG and Rxs values, data from sedimentation coefficients, and images of C 3 and C 3c seen by electron microscopy.

As a first step to validate the use of carbon nanotubes as novel vaccine or drug delivery devices, their interaction with a part of the human immune system, complement, has been explored. Haemolytic assays were conducted to investigate the activation of the human serum complement system via the classical and alternative pathways. Western blot and sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) techniques were used to elucidate the mechanism of activation of complement via the classical pathway, and to analyse the interaction of complement and other plasma proteins with carbon nanotubes. We report for the first time that carbon nanotubes activate human complement via both classical and alternative pathways. We conclude that complement activation by nanotubes is consistent with reported adjuvant effects, and might also in various circumstances promote damaging effects of excessive complement activation, such as inflammation and granuloma formation. C1q binds directly to carbon nanotubes. Protein binding to carbon nanotubes is highly selective, since out of the many different proteins in plasma, very few bind to the carbon nanotubes. Fibrinogen and apolipoproteins (AI, AIV and CIII) were the proteins that bound to carbon nanotubes in greatest quantity.