Although rarely elicited during natural human infection, the most broadly neutralizing antibodies (BNAbs) against diverse human immunodeficiency virus (HIV)-1 strains target the membrane-proximal ectodomain region (MPER) of viral gp41. To gain insight into MPER antigenicity, immunogenicity, and viral function, we studied its structure in the lipid environment by a combination of nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR), and surface plasmon resonance (SPR) techniques. The analyses revealed a tilted N-terminal alpha helix (aa 664-672) connected via a short hinge to a flat C-terminal helical segment (675-683). This metastable L-shaped structure is immersed in viral membrane and, therefore, less accessible to immune attack. Nonetheless, the 4E10 BNAb extracts buried W672 and F673 after initial encounter with the surface-embedded MPER. The data suggest how BNAbs may perturb tryptophan residue-associated viral fusion involving the mobile N-terminal MPER segment and, given conservation of MPER sequences in HIV-1, HIV-2, and SIV, have important implications for structure-guided vaccine design.

The large-voltage hysteresis remains one of the biggest barriers to optimizing Li/Na-ion cathodes using lattice anionic redox reaction, despite their very high energy density and relative low cost. Very recently, a layered sodium cathode Na2Mn3O7 (or Na4/7Mn6/7□1/7O2, □ is vacancy) was reported to have reversible lattice oxygen redox with much suppressed voltage hysteresis. However, the structural and electronic structural origin of this small-voltage hysteresis has not been well understood. In this article, through systematic studies using ex situ/in situ electron paramagnetic resonance and X-ray diffraction, we demonstrate that the exceptional small-voltage hysteresis (<50 mV) between charge and discharge curves is rooted in the well-maintained oxygen stacking sequence in the absence of irreversible gliding of oxygen layers and cation migration from the transition-metal layers. In addition, we further identify that the 4.2 V charge/discharge plateau is associated with a zero-strain (de)­intercalation process of Na+ ions from distorted octahedral sites, while the 4.5 V plateau is linked to a reversible shrink/expansion process of the manganese-site vacancy during (de)­intercalation of Na+ ions at distorted prismatic sites. It is expected that these findings will inspire further exploration of new cathode materials that can achieve both high energy density and efficiency by using lattice anionic redox.

A vaccine capable of stimulating protective antiviral antibody responses is needed to curtail the global AIDS epidemic caused by HIV-1. Although rarely elicited during the course of natural infection or upon conventional vaccination, the membrane-proximal ectodomain region (MPER) of the HIV-1 glycoprotein of M r 41,000 (gp41) envelope protein subunit is the target of 3 such human broadly neutralizing antibodies (BNAbs): 4E10, 2F5, and Z13e1. How these BNAbs bind to their lipid-embedded epitopes and mediate antiviral activity is unclear, but such information might offer important insight into a worldwide health imperative. Here, EPR and NMR techniques were used to define the manner in which these BNAbs differentially recognize viral membrane-encrypted residues configured within the L-shaped helix-hinge-helix MPER segment. Two distinct modes of antibody-mediated interference of viral infection were identified. 2F5, like 4E10, induces large conformational changes in the MPER relative to the membrane. However, although 4E10 straddles the hinge and extracts residues W672 and F673, 2F5 lifts up residues N-terminal to the hinge region, exposing L669 and W670. In contrast, Z13e1 effects little change in membrane orientation or conformation, but rather immobilizes the MPER hinge through extensive rigidifying surface contacts. Thus, BNAbs disrupt HIV-1 MPER fusogenic functions critical for virus entry into human CD4 T cells and macrophages either by preventing hinge motion or by perturbing MPER orientation. HIV-1 MPER features important for targeted vaccine design have been revealed, the implications of which extend to BNAb targets on other viral fusion proteins.membrane-proximal ectodomain region ͉ neutralizing antibody ͉ vaccine design ͉ AIDS ͉ fusion T he 120-nm-diameter HIV-1 is a retrovirus that has a small genome consisting of 9 genes. The enveloped virion surface expresses the trimeric glycoprotein of M r 160,000 (gp160) spike protein, whose gp120 and gp41 subunits are assembled into noncovalently associated heterodimers. Unlike gp120, each gp41 subunit has a transmembrane segment (TM) that inserts into the membrane of the virus. The membrane proximal ectodomain region (MPER) links this TM to the folded gp41 ectodomain. Entry of HIV-1 into human T cells is mediated by attachment of the gp120 subunit to receptor CD4 and then binding to the coreceptor (CCR5 or CXCR4) (1). These interactions result in structural rearrangement of the gp41 subunit, followed by fusion of viral and host cell membranes (2, 3). Thus, antibody-mediated protection against HIV-1 must target the gp120/gp41 envelope trimer, the only viral protein exposed on the virion surface.Although high-titer, strain-specific neutralizing antibodies are readily generated during the course of natural infection or against subunit vaccines, broadly neutralizing antibodies (BNAbs), in contrast, are rarely produced (reviewed in ref. 4). Sequence variability, extensive glycosylation, and immunodominance of those exposed, largely variable segments subvert immune res...

We have performed temperature-dependent electron spin resonance (ESR) measurements of the stable free radical trityl OX063, an efficient polarizing agent for dissolution dynamic nuclear polarization (DNP), at the optimum DNP concentration (15 mM). We have found that (i) when compared to the W-band electron spin-lattice relaxation rate T1e−1 of other free radicals used in DNP at the same concentration, trityl OX063 has slower T1e−1 than BDPA and 4-oxo-TEMPO. At T> 20 K, the T1e−1 vs T data of trityl OX063 appears to follow a power law dependence close to the Raman process prediction whereas at T<10 K, electronic relaxation slows and approaches the direct process behaviour. (ii) Gd3+ doping, a factor known to enhance DNP, of trityl OX063 samples measured at W-band resulted in monotonic increases of T1e−1 especially at temperatures below 20–40 K while the ESR lineshapes remained essentially unchanged. (iii) The high frequency ESR spectrum can be fitted with an axial g-tensor with a slight g-anisotropy: gx=gy=2.00319(3) and gz=2.00258(3). Although the ESR linewidth D monotonically increases with field, the temperature-dependent T1e −1 is almost unchanged as the ESR frequency is increased from 9.5 GHz to 95 GHz, but becomes faster at 240 GHz and 336 GHz. The ESR properties of trityl OX063 reported here may provide insights into the efficiency of DNP of low-γ nuclei performed at various magnetic fields, from 0.35 T to 12 T.