The A1 domain in VWF tubules. (A) Atomic sphere representation of D-assembly tubules (left)¹⁴ and tubules containing the A1 domain, colored chartreuse (right). (B) Details of the 2 interfaces between A1 and the D-assemblies in the tubule. Dashed lines represent potential hydrogen bonds between side chains and backbone atoms, which are not shown explicitly in the ribbon diagram. (C) Electron micrographs of negatively stained tubular assemblies formed upon incubation of D1D2 with the indicated VWF D′-A1 variants. Scale bar is 200 nm and applies to the 3 micrographs. (D) Denaturing, nonreducing polyacrylamide gel of the dimeric, disulfide-bonded D’-A1 samples used for the experiment shown in panel C.