Betanodaviruses cause massive mortality in marine fish species with viral nervous necrosis. The structure of a T = 3 Grouper nervous necrosis virus-like particle (GNNV-LP) is determined by the ab ...initio method with non-crystallographic symmetry averaging at 3.6 Å resolution. Each capsid protein (CP) shows three major domains: (i) the N-terminal arm, an inter-subunit extension at the inner surface; (ii) the shell domain (S-domain), a jelly-roll structure; and (iii) the protrusion domain (P-domain) formed by three-fold trimeric protrusions. In addition, we have determined structures of the T = 1 subviral particles (SVPs) of (i) the delta-P-domain mutant (residues 35-217) at 3.1 Å resolution; and (ii) the N-ARM deletion mutant (residues 35-338) at 7 Å resolution; and (iii) the structure of the individual P-domain (residues 214-338) at 1.2 Å resolution. The P-domain reveals a novel DxD motif asymmetrically coordinating two Ca2+ ions, and seems to play a prominent role in the calcium-mediated trimerization of the GNNV CPs during the initial capsid assembly process. The flexible N-ARM (N-terminal arginine-rich motif) appears to serve as a molecular switch for T = 1 or T = 3 assembly. Finally, we find that polyethylene glycol, which is incorporated into the P-domain during the crystallization process, enhances GNNV infection. The present structural studies together with the biological assays enhance our understanding of the role of the P-domain of GNNV in the capsid assembly and viral infection by this betanodavirus.
Understanding the structural diversity of honeybee-infecting viruses is critical to maintain pollinator health and manage the spread of diseases in ecology and agriculture. We determine cryo-EM ...structures of T = 4 and T = 3 capsids of virus-like particles (VLPs) of Lake Sinai virus (LSV) 2 and delta-N48 LSV1, belonging to tetraviruses, at resolutions of 2.3-2.6 Å in various pH environments. Structural analysis shows that the LSV2 capsid protein (CP) structural features, particularly the protruding domain and C-arm, differ from those of other tetraviruses. The anchor loop on the central β-barrel domain interacts with the neighboring subunit to stabilize homo-trimeric capsomeres during assembly. Delta-N48 LSV1 CP interacts with ssRNA via the rigid helix α1', α1'-α1 loop, β-barrel domain, and C-arm. Cryo-EM reconstructions, combined with X-ray crystallographic and small-angle scattering analyses, indicate that pH affects capsid conformations by regulating reversible dynamic particle motions and sizes of LSV2 VLPs. C-arms exist in all LSV2 and delta-N48 LSV1 VLPs across varied pH conditions, indicating that autoproteolysis cleavage is not required for LSV maturation. The observed linear domino-scaffold structures of various lengths, made up of trapezoid-shape capsomeres, provide a basis for icosahedral T = 4 and T = 3 architecture assemblies. These findings advance understanding of honeybee-infecting viruses that can cause Colony Collapse Disorder.
The active site of methanol dehydrogenase (MDH) contains a rare disulfide bridge between adjacent cysteine residues. As a vicinal disulfide, the structure is highly strained, suggesting it might work ...together with the pyrroloquinoline quinone (PQQ) prosthetic group and the Ca2+ ion in the catalytic turnover during methanol (CH3OH) oxidation. We purify MDH from Methylococcus capsulatus (Bath) with the disulfide bridge broken into two thiols. Spectroscopic and high-resolution X-ray crystallographic studies of this form of MDH indicate that the disulfide bridge is redox active. We observe an internal redox process within the holo-MDH that produces a disulfide radical anion concomitant with a companion PQQ radical, as evidenced by an optical absorption at 408 nm and a magnetically dipolar-coupled biradical in the EPR spectrum. These observations are corroborated by electron-density changes between the two cysteine sulfurs of the disulfide bridge as well as between the bound Ca2+ ion and the O5–C5 bond of the PQQ in the high-resolution X-ray structure. On the basis of these findings, we propose a mechanism for the controlled redistribution of the two electrons during hydride transfer from the CH3OH in the alcohol oxidation without formation of the reduced PQQ ethenediol, a biradical mechanism that allows for possible recovery of the hydride for transfer to an external NAD+ oxidant in the regeneration of the PQQ cofactor for multiple catalytic turnovers. In support of this mechanism, a steady-state level of the disulfide radical anion is observed during turnover of the MDH in the presence of CH3OH and NAD+.
Monoclonal antibodies (mAbs) have gradually dominated the drug markets for various diseases. Improvement of the therapeutic activities of mAbs has become a critical issue in the pharmaceutical ...industry. A novel endo-β-N-acetylglucosaminidase, EndoSz, from Streptococcus equisubsp. zooepidemicus Sz105 is discovered and applied to enhance the activities of mAbs. Our studies demonstrate that the mutant EndoSz-D234M possesses an excellent transglycosylation activity to generate diverse glycoconjugates on mAbs. We prove that EndoSz-D234M can be applied to various marketed therapeutic antibodies and those in development for antibody remodeling. The remodeled homogeneous antibodies (mAb-G2S2) produced by EndoSz-D234M increase the relative ADCC activities by 3–26-fold. We further report the high-resolution crystal structures of EndoSz-D234M in the apo-form at 2.15 Å and the complex form with a bound G2S2-oxazoline intermediate at 2.25 Å. A novel pH-jump method was utilized to obtain the complex structure with a high resolution. The detailed interactions of EndoSz-D234M and the carried G2S2-oxazoline are hence delineated. The oxazoline sits in a hole, named the oxa-hole, which stabilizes the G2S2-oxazoline in transit and catalyzes the further transglycosylation reaction while targeting Asn-GlcNAc (+1) of Fc. In the oxa-hole, the H-bonding network involved with oxazoline dominates the transglycosylation activity. A mobile loop2 (a.a. 152–159) of EndoSz-D234M reshapes the binding grooves for the accommodation of G2S2-oxazoline upon binding, at which Trp154 forms a hydrogen bond with Man (−2). The long loop4 (a.a. 236–248) followed by helix3 is capable of dominating the substrate selectivity of EndoSz-D234M. In addition, the stepwise transglycosylation behavior of EndoSz-D234M is elucidated. Based on the high-resolution structures of the apo-form and the bound form with G2S2-oxazoline as well as a systematic mutagenesis study of the relative transglycosylation activity, the transglycosylation mechanism of EndoSz-D234M is revealed.
In
Pseudomonas aeruginosa
, an important opportunistic pathogen that causes numerous acute and chronic infections, the hybrid two-component system (TCS) regulates the swarming ability and biofilm ...formation with a multistep phosphorelay, and consists of hybrid-sensor histidine kinase (HK), histidine-containing phosphotransfer protein (Hpt) and response regulator (RR). In this work, two crystal structures of HptB and the receiver domain of HK PA1611 (PA1611REC) of
P. aeruginosa
have been determined in order to elucidate their interactions for the transfer of the phosphoryl group. The structure of HptB folds into an elongated four-helix bundle – helices α2, α3, α4 and α5, covered by the short N-terminal helix α1. The imidazole side chain of the conserved active-site histidine residue His57, located near the middle of helix α3, protrudes from the bundle and is exposed to solvent. The structure of PA1611REC possesses a conventional (β/α)
5
topology with five-stranded parallel β-sheets folded in the central region, surrounded by five α-helices. The divalent Mg
2+
ion is located in the negatively charged active-site cleft and interacts with Asp522, Asp565 and Arg567. The HptB–PA1611REC complex is further modeled to analyze the binding surface and interactions between the two proteins. The model shows a shape complementarity between the convex surface of PA1611REC and the kidney-shaped HptB with fewer residues and a different network involved in interactions compared with other TCS complexes, such as SLN1-R1/YPD1 from
Saccharomyces cerevisiae
and AHK5
RD
/AHP1 from
Arabidopsis thaliana
. These structural results provide a better understanding of the TCS in
P. aeruginosa
and could potentially lead to the discovery of a new treatment for infection.
Branched-chain aminotransferases (BCAT), which utilize pyridoxal 5′-phosphate (PLP) as a cofactor, reversibly catalyze the transfer of the α-amino groups of three of the most hydrophobic ...branched-chain amino acids (BCAA), leucine, isoleucine, and valine, to α-ketoglutarate to form the respective branched-chain α-keto acids and glutamate. The BCAT from Deinococcus radiodurans (DrBCAT), an extremophile, was cloned and expressed in Escherichia coli for structure and functional studies. The crystal structures of the native DrBCAT with PLP and its complexes with l-glutamate and α-ketoisocaproate (KIC), respectively, have been determined. The DrBCAT monomer, comprising 358 amino acids, contains large and small domains connected with an interdomain loop. The cofactor PLP is located at the bottom of the active site pocket between two domains and near the dimer interface. The substrate (l-glutamate or KIC) is bound with key residues through interactions of the hydrogen bond and the salt bridge near PLP inside the active site pocket. Mutations of some interaction residues, such as Tyr71, Arg145, and Lys202, result in loss of the specific activity of the enzymes. In the interdomain loop, a dynamic loop (Gly173 to Gly179) clearly exhibits open and close conformations in structures of DrBCAT without and with substrates, respectively. DrBCAT shows the highest specific activity both in nature and under ionizing radiation, but with lower thermal stability above 60°C, than either BCAT from Escherichia coli (eBCAT) or from Thermus thermophilus (HB8BCAT). The dimeric molecular packing and the distribution of cysteine residues at the active site and the molecular surface might explain the resistance to radiation but small thermal stability of DrBCAT.
Shrimp nodaviruses, including
(PvNV) and
nodaviruses (MrNV), cause white-tail disease in shrimps, with high mortality. The viral capsid structure determines viral assembly and host specificity during ...infections. Here, we show cryo-EM structures of
= 3 and
= 1 PvNV-like particles (PvNV-LPs), crystal structures of the protrusion-domains (P-domains) of PvNV and MrNV, and the crystal structure of the ∆N-ARM-PvNV shell-domain (S-domain) in
= 1 subviral particles. The capsid protein of PvNV reveals five domains: the P-domain with a new jelly-roll structure forming cuboid-like spikes; the jelly-roll S-domain with two calcium ions; the linker between the S- and P-domains exhibiting new cross and parallel conformations; the N-arm interacting with nucleotides organized along icosahedral two-fold axes; and a disordered region comprising the basic
-terminal arginine-rich motif (N-ARM) interacting with RNA. The N-ARM controls
= 3 and
= 1 assemblies. Increasing the
/
-termini flexibility leads to particle polymorphism. Linker flexibility may influence the dimeric-spike arrangement.
The protrusion domain (P-domain; MrNVPd) of Macrobrachium rosenbergii nodavirus (MrNV) exists in two conformations, parallel and X-shaped. We have performed a theoretical study to gain insight into ...the nature of the dimeric interactions involving the dimeric interfaces within parallel and X-shaped conformations of MrNVPd by applying the quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) analyses in the framework of the density functional theory (DFT) approach. The results reveal that the dimer–dimer interfaces of MrNVPd have hydrogen bonds of common types. Leu255–Lys287, Tyr257–Lys287, Lys287–Ser253, Met294–Cys328, Asp295–Lys327, Ser298–Ser324, Ile326–Asp295, and Cys328–Met294 are the key residue pairs of the dimer–dimer interfaces to maintain the dimer–dimer structures of MrNVPd through charge–charge, charge–dipole, dipole–dipole, hydrophobic, and hydrogen bonding interactions. The strengths of these intermolecular dimer–dimer interactions in the parallel conformation are much greater than those in the X-shaped conformation. The parallel trimeric interface is held basically by electrostatic and hydrophobic interactions. The electrostatic interactions accompanying a strong hydrogen bond of Oγ1–Hγ1···Oγ1 in the Thr276 A–Thr276 D pair maintain the intermolecular interface of two X-shaped MrNVPd dimers.
The alkaline α‐galactosidase AtAkαGal3 from Arabidopsis thaliana catalyzes the hydrolysis of α‐d‐galactose from galacto‐oligosaccharides under alkaline conditions. A phylogenetic analysis based on ...sequence alignment classifies AtAkαGal3 as more closely related to the raffinose family of oligosaccharide (RFO) synthases than to the acidic α‐galactosidases. Here, thin‐layer chromatography is used to demonstrate that AtAkαGal3 exhibits a dual function and is capable of synthesizing stachyose using raffinose, instead of galactinol, as the galactose donor. Crystal structures of complexes of AtAkαGal3 and its D383A mutant with various substrates and products, including galactose, galactinol, raffinose, stachyose and sucrose, are reported as the first representative structures of an alkaline α‐galactosidase. The structure of AtAkαGal3 comprises three domains: an N‐terminal domain with 13 antiparallel β‐strands, a catalytic domain with an (α/β)8‐barrel fold and a C‐terminal domain composed of β‐sheets that form two Greek‐key motifs. The WW box of the N‐terminal domain, which comprises the conserved residues FRSK75XW77W78 in the RFO synthases, contributes Trp77 and Trp78 to the +1 subsite to contribute to the substrate‐binding ability together with the (α/β)8 barrel of the catalytic domain. The C‐terminal domain is presumably involved in structural stability. Structures of the D383A mutant in complex with various substrates and products, especially the natural substrate/product stachyose, reveal four complete subsites (–1 to +3) at the catalytic site. A functional loop (residues 329–352) that exists in the alkaline α‐galactosidase AtAkαGal3 and possibly in RFO synthases, but not in acidic α‐galactosidases, stabilizes the stachyose at the +2 and +3 subsites and extends the catalytic pocket for the transferase mechanism. Considering the similarities in amino‐acid sequence, catalytic domain and activity between alkaline α‐galactosidases and RFO synthases, the structure of AtAkαGal3 might also serve a model for the study of RFO synthases, structures of which are lacking.
The alkaline α‐galactosidase AtAkαGal3 from Arabidopsis exhibits a dual function where it can synthesize stachyose using raffinose, instead of galactinol, as the galactose donor. Crystal structures of complexes of AtAkαGal3 and its D383A mutant with various substrates and products, including galactose, galactinol, raffinose, stachyose and sucrose, reveal four complete subsites (–1 to +3) and a new secondary product‐binding site, providing the first representative structure of an alkaline α‐galactosidase and a model for the raffinose family of oligosaccharide synthases.
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