Biology subjects

Smith, S. O.

Publications and source records attributed to Smith, S. O..

3 recordsLinked to original sources

bioRxiv2022

An electrostatic cluster guides Aβ40 fibril formation in cerebral amyloid angiopathy

Cerebral amyloid angiopathy (CAA) is associated with the accumulation of fibrillar A{beta} peptides upon and within the cerebral vasculature, which leads to loss of vascular integrity and contributes to disease progression in Alzheimers disease (AD). We investigate the structure of human-derived A{beta}40 fibrils obtained from patients diagnosed with sporadic or familial Dutch-type (E22Q) CAA. Using cryo-EM, two primary structures are identified containing elements that have not been observed in in vitro A{beta}40 fibril structures. One population has an ordered N-terminal fold comprised of two {beta}-strands stabilized by electrostatic interactions involving D1, E22, D23 and K28. This charged cluster is disrupted in the second population, which exhibits a disordered N-terminus and is favored in fibrils derived from the familial Dutch-type CAA patient. These results illustrate differences between human-derived CAA and AD fibrils, and how familial CAA mutations guide fibril formation.

neuroscience↗

bioRxiv2022

Constitutive Activation and Oncogenicity Are Mediated by Loss of Helical Structure at the Cytosolic Boundary of the Thrombopoietin Receptor

Dimerization of the thrombopoietin receptor (TpoR) is necessary for receptor activation and downstream signaling through activated Janus kinase 2. We have shown previously that different orientations of the transmembrane (TM) helices within a receptor dimer can lead to different signaling outputs. Here we addressed the structural basis of activation for receptor mutations S505N and W515K that induce myeloproliferative neoplasms. We show using in vivo bone marrow reconstitution experiments that ligand-independent activation of TpoR by TM asparagine (Asn) substitutions is proportional to the proximity of the mutation to the intracellular membrane surface. Solid-state NMR experiments on TM peptides indicate a progressive loss of helical structure in the juxtamembrane (JM) R/KWQFP motif with either proximity of Asn substitutions to the cytosolic boundary or mutation of W515 in the motif. Mutational studies in the TpoR cytosolic JM region show that the helical loss by itself can induce activation, but is localized to a maximum of 6 amino acids downstream of W515, the rest of the region until Box 1 requiring helicity for receptor function. The constitutive activation of TpoR mutants S505N and W515K can be inhibited by rotation of TM helices within the TpoR dimer, which also restores helicity around W515. Together these data allow us to develop a general model for activation and to explain the critical role of the JM W515 residue in the regulation of receptor activity. (Total manuscript without References and Figure Legends 6507 words, main text (without methods and materials):)

molecular biology↗

bioRxiv2020

Dimeric Transmembrane Orientations of APP/C99 Regulate γ-Secretase Processing Line Impacting Signaling and Oligomerization

Amyloid precursor protein (APP) cleavage by the {beta} secretase produces the C99 transmembrane (TM) protein, which contains three dimerization-inducing Gly-x-x-x-Gly motifs. We demonstrate that dimeric C99 TM orientations regulate the precise cleavage lines by {gamma}-secretase. Of all possible dimeric orientations imposed by a coiled coil to the C99 TM-cytosolic domain, the dimer (cc-del7) containing 33Gly-x-x-x-Gly37 in the interface promoted A{beta}42 processing line and AICD (APP Intracellular Domain)-dependent gene transcription, including BACE1 mRNA induction, enhancing amyloidogenic signaling. Another orientation exhibiting 25Gly-x-x-x-Gly29 in the interface (cc-del6) favored processing to A{beta}43/40, induced significantly less gene transcription, while promoting formation of SDS-resistant "A{beta}-like" oligomers, reminiscent of A{beta} peptide oligomers. These required both Val24 of a pro-{beta} motif and the 25Gly-x-x-x-Gly29 interface. Thus, crossing angles imposed by dimeric orientations give access to {gamma}-secretase at A{beta}48 or A{beta}49, linking the former to enhanced signaling and A{beta}42. We discuss avenues of blocking amyloidogenic processing.

neuroscience↗