Ribbons, multistranded

Multistranded cables and ribbons were also observed for calcitonin (Bauer et al, 1995). These appeared to contain laterally associated 8-nm-wide fibrils, whereas the diameter of the individual strands within the multistranded cables could not be measured directly from the images. To estimate this diameter, the authors plotted the helical crossover spacing of the cables as a function of their diameter. Using a linear regression fit, the data were extrapolated to zero, yielding a width of 4.1 nm, similar to the width of the single protofibrils (Fig. 2A Bauer et al., 1995). 

Even though for each peptide or protein the MPL value for the protofibril may be different, all the available data can be summarized in a fairly simple scheme. The basic subunit of all amyloid fibrils is a 4- to 5-nm-wide protofibril whose detailed molecular architecture is species dependent. All the other structures observed can be either described as ribbons, sheets, or multistranded cables of protofibrils (Fig. 3). 

Ribbons result from the lateral stacking of fibrils. They are observed rally after a prolonged heating at acid pH of globular proteins as different as LYS or P-Lg. The formation of multistranded ribbons occurs concomitantly with an extensive hydrolysis of the proteins into low molecular weight peptides [23]. Such small peptides are hypothesised to be responsible for the formation of multistranded ribbons. 

Lara C, Adamcik J, Jordens S et al (2011) General self-assembly mechanism converting hydrolyzed globular proteins into giant multistranded amyloid ribbons. Biomacromolecules 12 1868-1875... 

---