Blockade of the PD-1/PD-L1 immune checkpoint pathway with monoclonal antibodies has provided significant advances in cancer treatment. The antibody-based immunotherapies carry a number of disadvantages such as the high cost of the antibodies, their limited half-life, and immunogenicity. Development of small-molecule PD-1/PD-L1 inhibitors that could overcome these drawbacks is slow because of the incomplete structural information for this pathway. The first chemical PD-1/PD-L1 inhibitors have been recently disclosed by Bristol-Myers Squibb. Here we present NMR and X-ray characterization for the two classes of these inhibitors. The X-ray structures of the PD-L1/inhibitor complexes reveal one inhibitor molecule located at the center of the PD-L1 homodimer, filling a deep hydrophobic channel-like pocket between two PD-L1 molecules. Derivatives of (2-methyl-3-biphenylyl)methanol exhibit the structures capped on one side of the channel, whereas the compounds based on [3-(2,3-dihydro-1,4-benzodioxin-6-yl)-2-methylphenyl]methanol induce an enlarged interaction interface that results in the open "face-back" tunnel through the PD-L1 dimer.

Methyl moieties are highly valuable probes for quantitative NMR studies of large proteins.Hence, their assignment is of the utmost interest to obtain information on both interactions and dynamics of proteins in solution. Here, we present the synthesis of a new precursor that allows connection of leucine and valine pro-S methyl moieties to backbone atoms by linear 13 C-chains. This optimized 2 H/ 13 C-labelled acetolactate precursor can be combined with existing 13 C/ 2 Halanine and isoleucine precursors in order to directly transfer backbone assignment to the corresponding methyl groups. Using this simple approach leucine and valine pro-S methyl groups can be assigned using a single sample without requiring correction of 1 H/ 2 H isotopic shifts on 13 C resonances. The approach was demonstrated on the N-terminal domain of human HSP90, for which complete assignment of Ala-b, Ile-d 1 , Leu-d 2 , Met-e, Thr-g and Val-g 2 methyl groups was obtained.

Prefoldin is a heterohexameric protein assembly which acts as a co-chaperonin for the well conserved Hsp60 chaperonin, present in archaebacteria and the eukaryotic cell cytosol. Prefoldin is a holdase, capturing client proteins and subsequently transferring them to the Hsp60 chamber for refolding. The chaperonin family is implicated in the early stages of protein folding and plays an important role in proteostasis in the cytosol. Here, we report the assignment of 1 H N , 15 N, 13 C′, 13 C α , 13 C β , 1 H methyl , and 13 C methyl chemical shifts of the 87 kDa prefoldin from the hyperthermophilic archaeon Pyrococcus horikoshii, consisting of two α and four β subunits. 100% of the [ 13 C, 1 H]resonances of A b , I d1 , L d2 , T g2 , V g2 methyl groups were successfully assigned for both subunits.For the β-subunit, showing partial peak doubling, 80% of the backbone resonances were assigned.In the α subunit, large stretches of backbone resonances were not detectable due to slow (µs-ms) time scale dynamics. This conformational exchange limited the backbone sequential assignment of the α subunit to 57% of residues, which corresponds to 84% of visible NMR signals.