Altered N-glycan composition impacts flagella-mediated adhesion in Chlamydomonas reinhardtii

For the unicellular alga Chlamydomonas reinhardtii, the presence of N-glycosylated proteins on the surface of two flagella is crucial for both cell-cell interaction during mating and flagellar surface adhesion. However, it is not known whether only the presence or also the composition of N-glycans attached to respective proteins is important for these processes. To this end, we tested several C. reinhardtii insertional mutants and a CRISPR/Cas9 knockout mutant of xylosyltransferase 1A, all possessing altered N-glycan compositions. Taking advantage of atomic force microscopy and micropipette force measurements, our data revealed that reduction in N-glycan complexity impedes the adhesion force required for binding the flagella to surfaces. This results in impaired polystyrene bead binding and transport but not gliding of cells on solid surfaces. Notably, assembly, intraflagellar transport, and protein import into flagella are not affected by altered N-glycosylation. Thus, we conclude that proper N-glycosylation of flagellar proteins is crucial for adhering C. reinhardtii cells onto surfaces, indicating that N-glycans mediate surface adhesion via direct surface contact

A new, flexible n,n,n-tripodal facially capping ligand system: synthesis and structural characterization of beta-triketimines and their m(co)(3) complexes (m = cr, mo, w)

Reaction of imidoyl chlorides Ar*N=CCIR (Ar* = 2-iPrC(6)H(4), 2,6-iPr(2)C(6)H(3), 2-MeOC6H4; R = Me, Ph, tBu) with [Li(nacnac)] [nacnac = (Ar*NCMe)(2)CH] gives beta-triketimines L, most of which exist in solution in equilibrium with their imine/enamine tautomers. The route is highly modular, allowing independent variation of at least five parameters. The solution equilibria are very sensitive to such substituent pattern variation. Single-crystal X-ray diffraction analyses of examples of both tautomers and a geometric isomer in the solid state are presented, alongside solution NMR studies of the tautomerism. All examples revert exclusively to the beta-triimine form on complexation with M(CO)(3) fragments (M = Cr, Mo, W). Facial isomers result. The ligands are weak sigma-donors, as adjudged by CO IR stretching frequencies in [LM(CO)(3)], Crystal-structure determination on the isostructural pair [HC(2-iPrC(6)H(4)N=CMe)(3)M(CO)(3)] (M = Cr, Mo) revealed a hexagonal packing arrangement composed of aryl-aryl and carbonyl (CO)-H-C interactions which generates pseudocylindrical voids accounting for 6-9 % of the crystal volume. In only one case were these occupied by solvent molecules, This family of facially capping N,N,N-ligands with finely tunable bulk have wide potential in coordination chemistry