Transmembrane domain of IFITM3 is responsible for its interaction with influenza virus HA_(2) subunit

Interferon-inducible transmembrane protein 3(IFITM3)inhibits influenza virus infection by blocking viral membrane fusion,but the exact mechanism remains elusive.Here,we investigated the function and key region of IFITM3 in blocking influenza virus entry mediated by hemagglutinin(HA).The restriction of IFITM3 on HAmediated viral entry was confirmed by pseudovirus harboring HA protein from H5 and H7 influenza viruses.Subcellular co-localization and immunocoprecipitation analyses revealed that IFITM3 partially co-located with the full-length HA protein and could directly interact with HA_(2) subunit but not HA_(1) subunit of H5 and H7 virus.Truncated analyses showed that the transmembrane domain of the IFITM3 and HA_(2) subunit might play an important role in their interaction.Finally,this interaction of IFITM3 was also verified with HA_(2) subunits from other subtypes of influenza A virus and influenza B virus.Overall,our data demonstrate for the first time a direct interaction between IFITM3 and influenza HA protein via the transmembrane domain,providing a new perspective for further exploring the biological significance of IFITM3 restriction on influenza virus infection or HA-mediated antagonism or escape.

Translation rate underpins specific targeting of N-terminal transmembrane proteins to mitochondria

Protein biogenesis is a complex process,and complexity is greatly increased in eukaryotic cells through specific targeting of proteins to different organelles.To direct targeting,organellar proteins carry an organelle-specific targeting signal for recognition by organelle-specific import machinery.However,the situation is confusing for transmembrane domain(TMD)-containing signalanchored(SA)proteins of various organelles because TMDs function as an endoplasmic reticulum(ER)targeting signal.Although ER targeting of SA proteins is well understood,how they are targeted to mitochondria and chloroplasts remains elusive.Here,we investigated how the targeting specificity of SA proteins is determined for specific targeting to mitochondria and chloroplasts.Mitochondrial targeting requires multiple motifs around and within TMDs:a basic residue and an arginine-rich region flanking the N-and C-termini of TMDs,respectively,and an aromatic residue in the C-terminal side of the TMD that specify mitochondrial targeting in an additive manner.These motifs play a role in slowing down the elongation speed during translation,thereby ensuring mitochondrial targeting in a cotranslational manner.By contrast,the absence of any of these motifs individually or together causes at varying degrees chloroplast targeting that occurs in a post-translational manner.

Talin and kindlin： the one-two punch in integrin activation

Proper cell-cell and cell-matrix contacts mediated by integrin adhesion receptors are important for development, immune response, hemostasis and wound healing. Integrins pass trans-membrane signals bidirectionally through their regulated affinities for extracellular ligands and intracellular signaling molecules. Such bidirectional signaling by integrins is enabled by the conformational changes that are often linked among extracellular, transmembrane and cytoplasmic domains. Here, we review how talin-integrin and kindlin-integrin interactions, in cooperation with talin-lipid and kindlin-lipid interactions, regulate integrin affinities and how the progress in these areas helps us understand integrin-related diseases.

Functional expression and regulation of eukaryotic cytochrome P450 enzymes in surrogate microbial cell factories

Cytochrome P450(CYP)enzymes play crucial roles during the evolution and diversification of ancestral monocel-lular eukaryotes into multicellular eukaryotic organisms due to their essential functionalities including catalysis of housekeeping biochemical reactions,synthesis of diverse metabolites,detoxification of xenobiotics,and con-tribution to environmental adaptation.Eukaryotic CYPs with versatile functionalities are undeniably regarded as promising biocatalysts with great potential for biotechnological,pharmaceutical and chemical industry applica-tions.Nevertheless,the modes of action and the challenges associated with these membrane-bound proteins have hampered the effective utilization of eukaryotic CYPs in a broader range.This review is focused on comprehen-sive and consolidated approaches to address the core challenges in heterologous expression of membrane-bound eukaryotic CYPs in different surrogate microbial cell factories,aiming to provide key insights for better studies and applications of diverse eukaryotic CYPs in the future.We also highlight the functional significance of the previously underrated cytochrome P450 reductases(CPRs)and provide a rational justification on the progression of CPR from auxiliary redox partner to function modulator in CYP catalysis.