6fll | pdb_00006fll
SPECTROSCOPIC AND STRUCTURAL STUDY OF QW, A EGFP MUTANT SHOWING PHOTOSWITCHING PROPERTIES
Structural highlights
Function[B6F2F5_9ENTO] Capsid protein VP0: Component of immature procapsids, which is cleaved into capsid proteins VP4 and VP2 after maturation. Allows the capsid to remain inactive before the maturation step.[RuleBase:RU364118] Capsid protein VP1: Forms an icosahedral capsid of pseudo T=3 symmetry with capsid proteins VP2 and VP3. The capsid is 300 Angstroms in diameter, composed of 60 copies of each capsid protein and enclosing the viral positive strand RNA genome. Capsid protein VP1 mainly forms the vertices of the capsid. Capsid protein VP1 interacts with host cell receptor to provide virion attachment to target host cells. This attachment induces virion internalization. Tyrosine kinases are probably involved in the entry process. After binding to its receptor, the capsid undergoes conformational changes. Capsid protein VP1 N-terminus (that contains an amphipathic alpha-helix) and capsid protein VP4 are externalized. Together, they shape a pore in the host membrane through which viral genome is translocated to host cell cytoplasm. After genome has been released, the channel shrinks.[RuleBase:RU364118] Capsid protein VP2: Forms an icosahedral capsid of pseudo T=3 symmetry with capsid proteins VP2 and VP3. The capsid is 300 Angstroms in diameter, composed of 60 copies of each capsid protein and enclosing the viral positive strand RNA genome.[RuleBase:RU364118] Capsid protein VP3: Forms an icosahedral capsid of pseudo T=3 symmetry with capsid proteins VP2 and VP3. The capsid is 300 Angstroms in diameter, composed of 60 copies of each capsid protein and enclosing the viral positive strand RNA genome.[RuleBase:RU364118] Capsid protein VP4: Lies on the inner surface of the capsid shell. After binding to the host receptor, the capsid undergoes conformational changes. Capsid protein VP4 is released, Capsid protein VP1 N-terminus is externalized, and together, they shape a pore in the host membrane through which the viral genome is translocated into the host cell cytoplasm. After genome has been released, the channel shrinks.[RuleBase:RU364118] Protease 3C: cleaves host DDX58/RIG-I and thus contributes to the inhibition of type I interferon production. Cleaves also host PABPC1.[RuleBase:RU364118] Protein 2A: Cysteine protease that cleaves viral polyprotein and specific host proteins. It is responsible for the cleavage between the P1 and P2 regions, first cleavage occurring in the polyprotein. Cleaves also the host translation initiation factor EIF4G1, in order to shut down the capped cellular mRNA translation. Inhibits the host nucleus-cytoplasm protein and RNA trafficking by cleaving host members of the nuclear pores.[RuleBase:RU364118] Protein 2B: Plays an essential role in the virus replication cycle by acting as a viroporin. Creates a pore in the host reticulum endoplasmic and as a consequence releases Ca2+ in the cytoplasm of infected cell. In turn, high levels of cytoplasmic calcium may trigger membrane trafficking and transport of viral ER-associated proteins to viroplasms, sites of viral genome replication.[RuleBase:RU364118] Protein 2C: Induces and associates with structural rearrangements of intracellular membranes. Displays RNA-binding, nucleotide binding and NTPase activities. May play a role in virion morphogenesis and viral RNA encapsidation by interacting with the capsid protein VP3.[RuleBase:RU364118] Protein 3A: Localizes the viral replication complex to the surface of membranous vesicles. It inhibits host cell endoplasmic reticulum-to-Golgi apparatus transport and causes the dissassembly of the Golgi complex, possibly through GBF1 interaction. This would result in depletion of MHC, trail receptors and IFN receptors at the host cell surface.[RuleBase:RU364118] Protein 3AB: Localizes the viral replication complex to the surface of membranous vesicles. Together with protein 3CD binds the Cis-Active RNA Element (CRE) which is involved in RNA synthesis initiation. Acts as a cofactor to stimulate the activity of 3D polymerase, maybe through a nucleid acid chaperone activity.[RuleBase:RU364118] Protein 3CD: Is involved in the viral replication complex and viral polypeptide maturation. It exhibits protease activity with a specificity and catalytic efficiency that is different from protease 3C. Protein 3CD lacks polymerase activity. The 3C domain in the context of protein 3CD may have an RNA binding activity.[RuleBase:RU364118] RNA-directed RNA polymerase: Replicates the viral genomic RNA on the surface of intracellular membranes. May form linear arrays of subunits that propagate along a strong head-to-tail interaction called interface-I. Covalently attaches UMP to a tyrosine of VPg, which is used to prime RNA synthesis. The positive stranded RNA genome is first replicated at virus induced membranous vesicles, creating a dsRNA genomic replication form. This dsRNA is then used as template to synthesize positive stranded RNA genomes. ss(+)RNA genomes are either translated, replicated or encapsidated.[RuleBase:RU364118] Viral protein genome-linked: acts as a primer for viral RNA replication and remains covalently bound to viral genomic RNA. VPg is uridylylated prior to priming replication into VPg-pUpU. The oriI viral genomic sequence may act as a template for this. The VPg-pUpU is then used as primer on the genomic RNA poly(A) by the RNA-dependent RNA polymerase to replicate the viral genome. VPg may be removed in the cytoplasm by an unknown enzyme termed "unlinkase". VPg is not cleaved off virion genomes because replicated genomic RNA are encapsidated at the site of replication.[RuleBase:RU364118] Publication Abstract from PubMedReversibly photoswitchable fluorescent proteins (RSFPs) admirably combine the genetic encoding of fluorescence with the ability to repeatedly toggle between a bright and dark state, adding a new temporal dimension to the fluorescence signal. Accordingly, in recent years RSFPs have paved the way to novel applications in cell imaging that rely on their reversible photoswitching, including many super-resolution techniques such as F-PALM, RESOLFT, and SOFI that provide nanoscale pictures of the living matter. Yet many RSFPs have been engineered by a rational approach only to a limited extent, in the absence of clear structure-property relationships that in most cases make anecdotic the emergence of the photoswitching. We reported [ Bizzarri et al. J. Am Chem Soc. 2010 , 102 , 85 ] how the E222Q replacement is a single photoswitching mutation, since it restores the intrinsic cis-trans photoisomerization properties of the chromophore in otherwise nonswitchable Aequorea proteins of different color and mutation pattern (Q-RSFPs). We here investigate the subtle role of Q222 on the excited-state photophysics of the two simplest Q-RSFPs by a combined experimental and theoretical approach, using their nonswitchable anacestor EGFP as benchmark. Our findings link indissolubly photoswitching and Q222 presence, by a simple yet elegant scenario: largely twisted chromophore structures around the double bond (including hula-twist configurations) are uniquely stabilized by Q222 via H-bonds. Likely, these H-bonds subtly modulate the electronic properties of the chromophore, enabling the conical intersection that connects the excited cis to ground trans chromophore. Thus, Q222 belongs to a restricted family of single mutations that change dramatically the functional phenotype of a protein. The capability to distinguish quantitatively T65S/E222Q EGFP ("WildQ", wQ) from the spectrally identical EGFP by quantitative Optical Lock-In Detection (qOLID) witnesses the relevance of this mutation for cell imaging. Role of Gln222 in Photoswitching of Aequorea Fluorescent Proteins: A Twisting and H-Bonding Affair?,Storti B, Margheritis E, Abbandonato G, Domenichini G, Dreier J, Testa I, Garau G, Nifosi R, Bizzarri R ACS Chem Biol. 2018 Aug 17;13(8):2082-2093. doi: 10.1021/acschembio.8b00267. Epub, 2018 Jun 19. PMID:29878744[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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