Affinity maturation endows potent activity onto class 6 SARS-CoV-2 broadly neutralizing antibodies.

The emergence of SARS-CoV-2 variants of concern (VOCs) has greatly diminished the neutralizing activity of previously FDA-approved monoclonal antibodies (mAbs), including that of antibody cocktails and of first-generation broadly neutralizing antibodies such as S309 (Sotrovimab). In contrast, antibodies targeting cryptic conformational epitopes of the receptor binding domain (RBD) have demonstrated broad activity against emerging variants, but exert only moderate neutralizing activity, which has so far hindered clinical development. Here, we utilize in vitro display technology to identify and affinity-mature antibodies targeting the cryptic class 6 epitope, accessible only in the "up" conformation of the SARS-CoV-2 spike trimer.

The molecular structure of an axle-less F-ATPase.

FF ATP synthase is a molecular rotary motor that can generate ATP using a transmembrane proton motive force. Isolated F-ATPase catalytic cores can hydrolyse ATP, passing through a series of conformational states involving rotation of the central γ rotor subunit and the opening and closing of the catalytic β subunits. Cooperativity in F-ATPase has long thought to be conferred through the γ subunit, with three key interaction sites between the γ and β subunits being identified.

The series of conformational states adopted by rotorless F-ATPase during its hydrolysis cycle.

FF ATP synthase interchanges phosphate transfer energy and proton motive force via a rotary catalytic mechanism and isolated F-ATPase subcomplexes can also hydrolyze ATP to generate rotation of their central γ rotor subunit. As ATP is hydrolyzed, the F-ATPase cycles through a series of conformational states that mediates unidirectional rotation of the rotor. However, even in the absence of a rotor, the α and β subunits are still able to pass through a series of conformations, akin to those that generate rotation.

Molecular basis for GIGYF-TNRC6 complex assembly.

The GIGYF proteins interact with 4EHP and RNA-associated proteins to elicit transcript-specific translational repression. However, the mechanism by which the GIGYF1/2-4EHP complex is recruited to its target transcripts remain unclear. Here, we report the crystal structures of the GYF domains from GIGYF1 and GIGYF2 in complex with proline-rich sequences from the miRISC-binding proteins TNRC6C and TNRC6A, respectively.

Broadly neutralizing SARS-CoV-2 antibodies through epitope-based selection from convalescent patients.

Emerging variants of concern (VOCs) are threatening to limit the effectiveness of SARS-CoV-2 monoclonal antibodies and vaccines currently used in clinical practice; broadly neutralizing antibodies and strategies for their identification are therefore urgently required. Here we demonstrate that broadly neutralizing antibodies can be isolated from peripheral blood mononuclear cells of convalescent patients using SARS-CoV-2 receptor binding domains carrying epitope-specific mutations. This is exemplified by two human antibodies, GAR05, binding to epitope class 1, and GAR12, binding to a new epitope class 6 (located between class 3 and 5).

Changes within the central stalk of E. coli FF ATP synthase observed after addition of ATP.

FF ATP synthase functions as a biological generator and makes a major contribution to cellular energy production. Proton flow generates rotation in the F motor that is transferred to the F motor to catalyze ATP production, with flexible F/F coupling required for efficient catalysis. FF ATP synthase can also operate in reverse, hydrolyzing ATP and pumping protons, and in bacteria this function can be regulated by an inhibitory ε subunit.

The six steps of the complete F-ATPase rotary catalytic cycle.

FF ATP synthase interchanges phosphate transfer energy and proton motive force via a rotary catalysis mechanism. Isolated F-ATPase catalytic cores can hydrolyze ATP, passing through six intermediate conformational states to generate rotation of their central γ-subunit. Although previous structural studies have contributed greatly to understanding rotary catalysis in the F-ATPase, the structure of an important conformational state (the binding-dwell) has remained elusive.

Potent SARS-CoV-2 binding and neutralization through maturation of iconic SARS-CoV-1 antibodies.

Antibodies against coronavirus spike protein potently protect against infection and disease, but whether such protection can be extended to variant coronaviruses is unclear. This is exemplified by a set of iconic and well-characterized monoclonal antibodies developed after the 2003 SARS outbreak, including mAbs m396, CR3022, CR3014 and 80R, which potently neutralize SARS-CoV-1, but not SARS-CoV-2. Here, we explore antibody engineering strategies to change and broaden their specificity, enabling nanomolar binding and potent neutralization of SARS-CoV-2.

Structural analysis of the Sulfolobus solfataricus TF55β chaperonin by cryo-electron microscopy.

Chaperonins are biomolecular complexes that assist in protein folding. Thermophilic factor 55 (TF55) is a group II chaperonin found in the archaeal genus Sulfolobus that has α, β and γ subunits. Using cryo-electron microscopy, structures of the β-only complex of S.

Glutamate transporters have a chloride channel with two hydrophobic gates.

Glutamate is the most abundant excitatory neurotransmitter in the central nervous system, and its precise control is vital to maintain normal brain function and to prevent excitotoxicity. The removal of extracellular glutamate is achieved by plasma-membrane-bound transporters, which couple glutamate transport to sodium, potassium and pH gradients using an elevator mechanism. Glutamate transporters also conduct chloride ions by means of a channel-like process that is thermodynamically uncoupled from transport.

Cryo-EM structures provide insight into how E. coli FF ATP synthase accommodates symmetry mismatch.

FF ATP synthase functions as a biological rotary generator that makes a major contribution to cellular energy production. It comprises two molecular motors coupled together by a central and a peripheral stalk. Proton flow through the F motor generates rotation of the central stalk, inducing conformational changes in the F motor that catalyzes ATP production.

ATP Synthase: Expression, Purification, and Function.

ATP synthase is an essential enzyme found in all known forms of life, generating the majority of cellular energy via a rotary catalytic mechanism. Here, we describe the in-depth methods for expression, purification, and functional assessment of E. coli ATP synthase.

Cryo-EM reveals distinct conformations of ATP synthase on exposure to ATP.

ATP synthase produces the majority of cellular energy in most cells. We have previously reported cryo-EM maps of autoinhibited ATP synthase imaged without addition of nucleotide (Sobti et al. 2016), indicating that the subunit ε engages the α, β and γ subunits to lock the enzyme and prevent functional rotation.

Cryo-EM structures of the autoinhibited ATP synthase in three rotational states.

A molecular model that provides a framework for interpreting the wealth of functional information obtained on the F-ATP synthase has been generated using cryo-electron microscopy. Three different states that relate to rotation of the enzyme were observed, with the central stalk's ε subunit in an extended autoinhibitory conformation in all three states. The F motor comprises of seven transmembrane helices and a decameric c-ring and invaginations on either side of the membrane indicate the entry and exit channels for protons.

Rotary ATPases--dynamic molecular machines.

Recent work has provided the detailed overall architecture and subunit composition of three subtypes of rotary ATPases. Composite models of F-type, V-type and A-type ATPases have been constructed by fitting high-resolution X-ray structures of individual components into electron microscopy derived envelopes of the intact enzymes. Electron cryo-tomography has provided new insights into the supra-molecular arrangement of eukaryotic ATP synthases within mitochondria.

Rational-based protein engineering: tips and tools.

The rational engineering of proteins is driven by contemporary needs for new and altered biomolecular forms. Utilizing manipulative procedures of molecular biology, it is relatively straightforward to alter protein structure and function to create mutated or fused sequences. We here give an overview of procedures and strategies for site-directed mutagenesis, construction of fusion proteins, and insertion of tags.

Rotary ATPases: models, machine elements and technical specifications.

Rotary ATPases are molecular rotary motors involved in biological energy conversion. They either synthesize or hydrolyze the universal biological energy carrier adenosine triphosphate. Recent work has elucidated the general architecture and subunit compositions of all three sub-types of rotary ATPases.

Engineered rings of mixed yeast Lsm proteins show differential interactions with translation factors and U-rich RNA.

The Lsm proteins organize as heteroheptameric ring assemblies capable of binding RNA substrates and ancillary protein factors. We have constructed simplified Lsm polyproteins that organize as multimeric ring structures as analogues of the functional Lsm complexes. Polyproteins Lsm[2+3], Lsm[4+1], and Lsm[5+6] incorporate natural sequence extensions as linker peptides between the core Lsm domains.

Crystal structure of Lsm3 octamer from Saccharomyces cerevisiae: implications for Lsm ring organisation and recruitment.

Sm and Sm-like (Lsm) proteins are core components of the ribonucleoprotein complexes essential to key nucleic acid processing events within the eukaryotic cell. They assemble as polyprotein ring scaffolds that have the capacity to bind RNA substrates and other necessary protein factors. The crystal structure of yeast Lsm3 reveals a new organisation of the L/Sm beta-propeller ring, containing eight protein subunits.