Previous X-ray crystal structures have shown that linkers of five amino acid 
residues connecting pairs of chicken brain alpha-spectrin and human erythroid 
beta-spectrin repeats can undergo bending without losing their alpha-helical 
structure. To test whether bending at one linker can influence bending at an 
adjacent linker, the structures of two and three repeat fragments of chicken 
brain alpha-spectrin have been determined by X-ray crystallography. The 
structure of the three-repeat fragment clearly shows that bending at one linker 
can occur independently of bending at an adjacent linker. This observation 
increases the possible trajectories of modeled chains of spectrin repeats. 
Furthermore, the three-repeat molecule crystallized as an antiparallel dimer 
with a significantly smaller buried interfacial area than that of alpha-actinin, 
a spectrin-related molecule, but large enough and of a type indicating 
biological specificity. Comparison of the structures of the spectrin and 
alpha-actinin dimers supports weak association of the former, which could not be 
detected by analytical ultracentrifugation, versus strong association of the 
latter, which has been observed by others. To correlate features of the 
structure with solution properties and to test a previous model of stable 
spectrin and dystrophin repeats, the number of inter-helical interactions in 
each repeat of several spectrin structures were counted and compared to their 
thermal stabilities. Inter-helical interactions, but not all interactions, 
increased in parallel with measured thermal stabilities of each repeat and in 
agreement with the thermal stabilities of two and three repeats and also partial 
repeats of spectrin.