Biology subjects

Schiller, N.

Publications and source records attributed to Schiller, N..

3 recordsLinked to original sources

bioRxiv2019

Structural and mutational analysis of the ribosome-arresting human XBP1u

XBP1u, a central component of the unfolded protein response (UPR), is a mammalian protein containing a functionally critical translational arrest peptide (AP). Here, we present a 3 [A] cryo-EM structure of the stalled human XBP1u AP. It forms a unique turn in the upper part of the ribosomal exit tunnel and causes a subtle distortion of the peptidyl transferase center, explaining the temporary translational arrest induced by XBP1u. During ribosomal pausing the hydrophobic region 2 (HR2) of XBP1u is recognized by SRP, but fails to efficiently gate the Sec61 translocon. An exhaustive mutagenesis scan of the XBP1u AP revealed that only 10 out of 21 mutagenized positions in the XBP1u AP are optimal with respect to translational arrest activity. Thus, XBP1u has evolved to induce an intermediate level of translational arrest, allowing efficient targeting by SRP without activating the Sec61 channel and thereby serving its central function in the UPR.

biochemistry↗

bioRxiv2018

Astrotactins 1 and 2 have similar membrane topology and mature via endoproteolytic cleavage catalyzed by signal peptidase

Astrotactins 1 and 2 (Astn1, Astn2) are membrane proteins that function in glial-guided migration, receptor trafficking and synaptic plasticity in brain, as well as in planar polarity pathways in skin. Here, we have mapped the topologies of mouse Astn1 and Astn2 in rough microsomal membranes (RMs) using glycosylation mapping and protease-protection assays, and find that Astn2 has a cleaved N-terminal signal peptide (SP), an N-terminal domain located in the lumen of the RMs (topologically equivalent to the extracellular surface in cells), two transmembrane helices (TMHs), and a large C-terminal lumenal domain. We find that Astn1 has the same topology as Astn2 but see no evidence of SP cleavage. Both Astn1 and Astn2 mature through endoproteolytic cleavage in the second TMH; importantly, we identify the endoprotease responsible for the maturation of Astn1 and Astn2 as signal peptidase. Differences in the degree of the maturation of Astn1 and Astn2 possibly contribute to the higher levels of the C-terminal domain of Astn1 detected on the CNS neuronal membranes and to the different functions of Astn1 and Astn2.

neuroscience↗

bioRxiv2017

Mutational analysis of the human Xbp1 translational arrest peptide and construction of arrest-enhanced variants

Xbp1, a protein involved in the unfolded protein response, is a rare example of a mammalian protein that contains a well-defined translational arrest peptide (AP). In order to define the critical residues in the Xbp1u AP, and to search for variants with stronger arrest potency than the wildtype Xbp1u AP, we have carried out a full mutagenesis scan where each residue in the AP was replaced by the other 19 natural amino acids. We find that 10 of the 21 mutagenized positions are optimal already in the wildtype Xbp1 AP, while certain mutations in the remaining residues lead to a strong increase in the arrest potency. Xbp1 has thus evolved to induce an intermediate level of translational arrest, and versions with much stronger arrest efficiency exist. We further show Xbp1-induced translational arrest is reduced in response to increased tension in the nascent chain, making it possible to carry out studies in mammalian systems of cotranslational processes such as membrane protein assembly and protein folding by using suitable Xbp1 AP variants as \"force sensors\", as has been done previously in E. coli using bacterial APs.

molecular biology↗