Systemic amyloidosis is caused by the misfolding of a circulating amyloid precursor protein and the deposition of amyloid fibrils in multiple organs. Chemical and biophysical analysis of amyloid fibrils from human AL and murine AA amyloidosis reveal the same fibril morphologies in different tissues or organs of one patient or diseased animal. The observed structural similarities concerned the fibril morphology, the fibril protein primary and secondary structures, the presence of post-translational modifications and, in case of the AL fibrils, the partially folded characteristics of the polypeptide chain within the fibril. Our data imply for both analyzed forms of amyloidosis that the pathways of protein misfolding are systemically conserved; that is, they follow the same rules irrespective of where inside one body fibrils are formed or accumulated.
Listeria monocytogenes is a devastating bacterial pathogen. Its virulence and intracellular stress tolerance are supported by caseinolytic protease P (ClpP), an enzyme that is conserved among bacteria. L. monocytogenes expresses two ClpP isoforms that are only distantly related by sequence and differ in catalysis, oligomerization, active-site composition, and N-terminal interaction sites for associated AAA(+) chaperones. The crystal structure of the ClpP1/2 heterocomplex from L. monocytogenes was solved, and in combination with biochemical studies, it provides insights into the mode of action. The results demonstrate that structural interlocking of LmClpP1 with LmClpP2 leads to the formation of a tetradecamer, aligns all 14 active sites, and enhances proteolytic activity. Furthermore, the catalytic center was identified as being responsible for the transient stability of ClpPs.
Caseinolytic protease P (ClpP) is an important regulator of Staphylococcus aureus pathogenesis. A high-throughput screening for inhibitors of ClpP peptidase activity led to the identification of the first non-covalent binder for this enzyme class. Co-crystallization of the small molecule with S. aureus ClpP revealed a novel binding mode: Because of the rotation of the conserved residue proline 125, ClpP is locked in a defined conformational state, which results in distortion of the catalytic triad and inhibition of the peptidase activity. Based on these structural insights, the molecule was optimized by rational design and virtual screening, resulting in derivatives exceeding the potency of previous ClpP inhibitors. Strikingly, the conformational lock is overturned by binding of ClpX, an associated chaperone that enables proteolysis by substrate unfolding in the ClpXP complex. Thus, regulation of inhibitor binding by associated chaperones is an unexpected mechanism important for ClpP drug development.
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