bims-nucpor 2021-07-11 papers

Issue of 2021–07–11
three papers selected by
Sara Mingu, Johannes Gutenberg University

Biophys J. 2021 Jul 05. pii: S0006-3495(21)00533-6. [Epub ahead of print]

FG Nucleoporins feature unique amino acid sequence patterns that distinguish them from other IDPs.

Mohaddeseh Peyro, Mohammad Soheilypour, Vikrum S Nibber, Andrew M Dickson, Mohammad R K Mofrad.

FG Nucleoporins (FG Nups) are intrinsically disordered proteins and are the putative regulators of nucleocytoplasmic transport. They allow fast, yet selective transport of molecules through the nuclear pore complex (NPC), but the underlying mechanism of nucleocytoplasmic transport is not yet fully discovered. As a result, FG Nups have been the subject of extensive research in the past two decades. While most studies have been focused on analyzing the conformation and function of FG Nups from a biophysical standpoint, some recent studies have investigated the sequence-function relationship of FG Nups, with a few investigating amino acid sequences of a large number of FG Nups to understand common characteristics that might enable their function. Previously, we identified an evolutionarily conserved feature in FG Nup sequences, which are extended sub-sequences with low charge density, containing only positive charges, and located toward the N-terminus of FG Nups. We named these patterns longest positive like charge regions (lpLCRs). These patterns are specific to positively charged residues and negatively charged residues do not demonstrate such a pattern. In this study, we compare FG Nups with other disordered proteins obtained from the DisProt and UniProt database, in terms of presence of lpLCRs. Our results show that the lpLCRs are virtually exclusive to FG Nups and are not observed in other disordered proteins. Also, lpLCRs are what differentiate FG Nups from DisProt proteins in terms of charge distribution, meaning that excluding lpLCRs from the sequences of FG Nups make them similar to Disprot proteins in terms of charge distribution. We also previously showed the biophysical effect of lpLCRs in conformation of FG Nups. The results of this study are in line with our previous findings and imply that lpLCRs are virtually exclusive and functionally significant characteristics of FG Nups and nucleocytoplasmic transport.

DOI: https://doi.org/10.1016/j.bpj.2021.06.031

J Biochem. 2021 Jun 12. pii: mvab072. [Epub ahead of print]

Karyopherin-βs play a key role as a phase separation regulator.

Takuya Yoshizawa, Lin Guo.

Recent studies have revealed that cells utilize liquid-liquid phase separation (LLPS) as a mechanism in assembly of membrane-less organelles, such as RNP granules. The nucleus is a well-known membrane-bound organelle surrounded by the nuclear envelope; the nuclear pore complex on the nuclear envelope likely applies LLPS in the central channel to facilitate selective biological macromolecule exchange. Karyopherin-β family proteins exclusively pass through the central channel with cargos by dissolving the phase separated hydrogel formed by the phenylalanine-glycine (FG) repeats-containing nucleoporins. Karyopherin-βs also exhibit dissolution activity for the phase separation of cargo proteins. Many cargos, including RNA-binding proteins containing intrinsically disordered regions (IDRs), undergo phase separation; however, aberrant phase separation is linked to fatal neurodegenerative diseases. Multiple weak interactions between karyopherin-βs and phase separation-prone proteins, such as FG repeats-containing nucleoporins or IDR-containing karyopherin-β cargos, are likely to be important for passing through the nuclear pore complex and maintaining the soluble state of cargo, respectively. In this review, we discuss how karyopherin-βs regulate phase separation to function.

Keywords: RNA binding proteins; karyopherin-βs; liquid–liquid phase separation; low-complexity domain; neurodegenerative disease

DOI: https://doi.org/10.1093/jb/mvab072

Nucleic Acids Res. 2021 Jul 07. pii: gkab579. [Epub ahead of print]

Translation mediated by the nuclear cap-binding complex is confined to the perinuclear region via a CTIF-DDX19B interaction.

Yeonkyoung Park, Joori Park, Hyun Jung Hwang, Leehyeon Kim, Kwon Jeong, Hyun Kyu Song, Simone C Rufener, Oliver Mühlemann, Yoon Ki Kim.

Newly synthesized mRNA is translated during its export through the nuclear pore complex, when its 5'-cap structure is still bound by the nuclear cap-binding complex (CBC), a heterodimer of cap-binding protein (CBP) 80 and CBP20. Despite its critical role in mRNA surveillance, the mechanism by which CBC-dependent translation (CT) is regulated remains unknown. Here, we demonstrate that the CT initiation factor (CTIF) is tethered in a translationally incompetent manner to the perinuclear region by the DEAD-box helicase 19B (DDX19B). DDX19B hands over CTIF to CBP80, which is associated with the 5'-cap of a newly exported mRNA. The resulting CBP80-CTIF complex then initiates CT in the perinuclear region. We also show that impeding the interaction between CTIF and DDX19B leads to uncontrolled CT throughout the cytosol, consequently dysregulating nonsense-mediated mRNA decay. Altogether, our data provide molecular evidence supporting the importance of tight control of local translation in the perinuclear region.

DOI: https://doi.org/10.1093/nar/gkab579