How ligand binding alters integrin conformation in outside-in signaling, and how inside-out signals alter integrin affinity for ligand, have been mysterious. We address this with electron microscopy, physicochemical measurements, mutational introduction of disulfides, and ligand binding to alphaVbeta3 and alphaIIbbeta3 integrins. We show that a highly bent integrin conformation is physiological and has low affinity for biological ligands. Addition of a high affinity ligand mimetic peptide or Mn(2+) results in a switchblade-like opening to an extended structure. An outward swing of the hybrid domain at its junction with the I-like domain shows conformational change within the headpiece that is linked to ligand binding. Breakage of a C-terminal clasp between the alpha and beta subunits enhances Mn(2+)-induced unbending and ligand binding.

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Two mutations in the a-synuclein gene (A30P and A53T) have been linked to autosomal dominant early-onset Parkinson's disease (PD). Both mutations promote the formation of transient protofibrils (prefibrillar oligomers), suggesting that protofibrils are linked to cytotoxicity. In this work, the effect of these mutations on the structure of a-synuclein oligomers was investigated using electron microscopy and digital image processing. The PD-linked mutations (A30P and A53T) were observed to affect both the morphology and the size distribution of a-synuclein protofibrils (measured by analytical ultracentrifugation and scanning transmission electron microscopy). The A30P variant was observed to promote the formation of annular, pore-like protofibrils, whereas A53T promotes formation of annular and tubular protofibrillar structures. Wild-type a-synuclein also formed annular protofibrils, but only after extended incubation. The formation of pore-like oligomeric structures may explain the membrane permeabilization activity of a-synuclein protofibrils. These structures may contribute to the pathogenesis of PD.

Adjustable-length loop devices may need to be retensioned after cycling the knee and fixing the tibial side to account for the increased initial displacement seen with these devices.