Ribonuclease Activity of an Artificial Catalyst That Combines a Ligated Cu^II Ion and a Guanidinium Group at the Upper Rim of a <i>cone</i>-Calix[4]arene Platform

A <i>cone</i>-calix­[4]­arene derivative, featuring a guanidinium group and a Cu^II ion ligated to a 1,4,7-triazacyclononane (TACN) ligand at the 1,3-distal positions of the upper rim, effectively catalyzes the cleavage of 2-hydroxypropyl <i>p</i>-nitrophenyl phosphate (HPNP) and a number of diribonucleoside 3′,5′-monophosphates (<i>N</i>p<i>N</i>′). Kinetic and potentiometric measurements support the operation of a general-base/general-acid mechanism and demonstrate that the hydroxo form of the ligated Cu^II ion is the sole catalytically active species. Rate enhancements relative to the background hydrolysis reaction at 1 mM catalyst concentration are 6 × 10⁵-fold for HPNP and cluster around 10⁷-fold with the most favorable catalyst–<i>N</i>p<i>N</i>′ combinations

Phosphonated Calixarene as a “Molecular Glue” for Protein Crystallization

Protein crystallization remains a serious bottleneck to structure determination by X-ray diffraction methods. Compounds acting as “molecular glue” provide a promising strategy to overcome this bottleneck. Such molecules interact via noncovalent bonds with two or more protein surfaces to promote lattice formation. Here, we report a 1.5 Å resolution crystal structure of lysine-rich cytochrome <i>c</i> complexed with <i>p</i>-phosphonatomethyl-calix­[4]­arene (<b>pmclx</b>_<b>4</b>). Evidence for complex formation in solution was provided by NMR studies. Similar to <i>p</i>-sulfonato-calix­[4]­arene (<b>sclx</b>_<b>4</b>), the cavity of <b>pmclx</b>_<b>4</b> entrapped a single lysine side chain. Interesting features of protein recognition by the phosphonate substituents were identified in the crystal structure. A new calixarene binding site was identified at Lys54. The electron density at this site indicated two distinct calixarene conformers, suggesting a degree of ligand mobility. The role of <b>pmclx</b>_<b>4</b> in protein crystal packing (molecular glue and patchy particle model) as well as differences in protein-binding with respect to <b>sclx</b>_<b>4</b> are discussed

image_1_Circulating Follicular Helper and Follicular Regulatory T Cells Are Severely Compromised in Human CD40 Deficiency: A Case Report.pdf

<p>Mutations in genes that control class switch recombination and somatic hypermutation during the germinal center (GC) response can cause diverse immune dysfunctions. In particular, mutations in CD40LG, CD40, AICDA, or UNG cause hyper-IgM (HIGM) syndrome, a heterogeneous group of primary immunodeficiencies. Follicular helper (Tfh) and follicular regulatory (Tfr) T cells play a key role in the formation and regulation of GCs, but their role in HIGM pathogenesis is still limited. Here, we found that compared to CD40 ligand (CD40L)- and activation-induced cytidine deaminase (AICDA)-deficient patients, circulating Tfh and Tfr cells were severely compromised in terms of frequency and activation phenotype in a child with CD40 deficiency. These findings offer useful insight for human Tfh biology, with potential implications for understanding the molecular basis of HIGM syndrome caused by mutations in CD40.</p