Marcus C. Durrant

Structure–Function Analysis of Cf-9, a Receptor-Like Protein with Extracytoplasmic Leucine-Rich Repeats

The tomato (Lycopersicon pimpinellifolium) resistance protein Cf-9 belongs to a large class of plant proteins with extracytoplasmic Leu-rich repeats (eLRRs). eLRR proteins play key roles in plant defense and development, mainly as receptor-like proteins or receptor-like kinases, conferring recognition of various pathogen molecules and plant hormones. We report here a large-scale structure–function analysis of an eLRR protein. A total of 66 site-directed mutants of Cf-9 were analyzed for activity in Avr9 recognition and for protein stability and the results interpreted with the help of a homology model of the Cf-9 structure. Conserved Trp and Cys pairs in the N-terminal LRR-flanking domain appear to be important for Cf-9 activity and are probably exposed at the putative concave inner surface of the Cf-9 protein, where recognition specificity also resides. Removal of each of the 22 putative N-linked glycosylation sites (PGS) revealed that many PGSs contribute to Cf-9 activity and that the PGSs in the putative α-helices of the LRR modules are essential. Immunoblot analysis and mass spectrometry showed that all but one of the PGSs are N-glycosylated. Introduction of glycosylation at the putative concave β-sheet surface blocks Cf-9 activity, in some cases probably by disturbing specific recognition, and in another case by steric hindrance with existing N-glycans. The glycosylation pattern and several other features are conserved in other eLRR proteins, where similar mutations show similar phenotypes.

A molybdenum-centred model for nitrogenase catalysis

Abstract Density functional theory has been used to relate the intrinsic N2 binding affinities of the Fe and Mo sites of the iron–molybdenum cofactor of nitrogenase (FeMoco) to those of known N2 complexes. The results indicate that initial N2 binding to FeMoco is reversible, and that Mo is the preferred site. A mechanism for N2 reduction is proposed in which a partially reduced MoNNH2 species undergoes cleavage across a MoFeS2 face of FeMoco.

Synthesis and characterization of the seven-coordinate complexes [MI] (M = Mo or W)

Abstract Equimolar quantities of seven-coordinate complexes [MI] (M = Mo or W) and Ph P(S)CH P(S)Ph reacted in CH C1 at room temperature giving the new acetonitrile-displaced products [MI (CO) Ph P(S)CH P(S)Ph-S,S], (1) and (2), in good yield. The tungsten complex 2, reacted with one equivalent of Ph PCH PPh giving the bis(diphenylphosphino)methane complex [WI (CO) (Ph PCH PPh]. Copyright

Seven-coordinate bromocarbonyl complexes of molybdenum(II) and tungsten(II) containing neutral sulfur donor ligands: crystal structure of [WBr2(CO)3{PhS(CH2)2SPh-S,S′}]

Abstract Treatment of [MBr 2 (CO) 3 (NCMe) 2 ] (M = Mo or W) with a slight excess of RS(CH 2 ) 2 SR (R = Ph, C 6 H 4 F-4) in CH 2 Cl 2 at room temperature gave the acetonitrile displaced products [MBr 2 (CO) 3 {RS(CH 2 ) 2 SR- S , S ′}]. The complex with M = W, R = Ph was crystallographically characterised and has a distorted capped octahedral geometry with one carbonyl group in the capping position, two carbonyls and one sulfur atom in the capped face, and one sulfur and two bromines in the uncapped face. Reaction of [WBr 2 (CO) 3 (NCMe) 2 ] with two equivalents of RS(CH 2 ) 2 SR in CH 2 Cl 2 at room temperature gives the cationic complexes [WBr(CO) 3 {RS(CH 2 ) 2 - S }{RS- S , S ′}] Br. Similarly, treatment of [WBr 2 (CO 3 )(NCMe) 2 ] with one and two equivalents of Ph 2 P(S)CH 2 P(S)Ph 2 in CH 2 Cl 2 at room temperature afforded [WBr 2 (CO) 3 {Ph 2 P(S)CH 2 P(S)Ph 2 - S , S ′}] and [WBr(CO) 3 {Ph 2 P(S)CH 2 P(S)Ph 2 - S }{Ph 2 P(S)CH 2 P(S)Ph 2 - S , S ′}] Br respec Reaction of [MBr 2 (CO) 3 (NCMe) 2 ] with one equivalent of MeS(CH 2 ) 2 SMe in CH 2 Cl 2 at room temperature gave [MoBr 2 (CO) 2 {MeS(CH 2 ) 2 S(CH 2 ) 2 SMe- S , S ′, S ″}] and [Br 2 (CO) 3 {MeS(CH 2 ) 2 S(CH 2 ) 2 SMe - S , S ′}] respectively. Finally, reaction of equimolar quantities of [MoBr 2 (CO) 2 (NCMe) 2 ] and ttob (tobb = 2,5,8-trithia[9]- o -benzenophane) gives the S 3 bonded complex [MoBr 2 (CO) 2 (ttob- S , S ′, S ″)].

Synthesis and crystal structures of the distorted pentagonal bipyramidal seven-coordinate acetylacetonate complexes [MI(acac)(CO)2(PEt3)2] (M = Mo or W)

Equimolar quantities of [MI 2 (CO) 3 (PEt 3 ) 2 ] (M = Mo or W) and Na[acac] react in a Et 2 O/CH 2 Cl 2 /EtOH mixture at room temperature to give high yields of the seven-coordinate complexes [MI(acac)(CO) 2 (PEt 3 ) 2 ] ( 1 and 2 ). The crystal structures of 1 and 2 , while not isomorphous, show similar seven-coordination geometries with the acetylacetonate ligand coordinating in a bidentate manner. The geometry around these complexes can best be described as distorted pentagonal bipyramidal with one carbonyl and iodine in the axial positions and the acetylacetonate ligand, two phosphine ligands and one carbonyl group in equatorial positions. Spectroscopic data for 1 and 2 are reported.

A new class of derivatisable tripodal ligand. X-ray crystal structure of [Cu(SO4)(tpm)(H2O)] (tpm=1,1,1-tris(2-pyridyl)methylamine)

Abstract 1,1-Bis(2-pyridyl)methylamine, 1,1,1-tris(2-pyridyl)methylamine (tpm), 2-methylsulfanyl-1,1-bis(2-pyridyl)ethylamine and related compounds have been prepared by metallation of 2-aminomethylpyridine. Tpm coordinates readily to both copper(I) and copper(II); the X-ray crystal structure of the copper(II) sulfato complex [Cu(SO4)(tpm)(H2O)] shows the tpm ligand coordinated to the metal via the three pyridine nitrogens in a tripodal fashion, leaving the primary amine function free for derivatisation.

Bis(2,2′‐bi­pyridine)­nitratocopper(II) nitrate

The title complex, [Cu(C10H8N2)2(NO3)]NO3, is the first reported unsolvated [Cu(bipy)2(NO3)]NO3 structure (bipy is 2,2′-bixadpyridine). The CuII atom of the [Cu(bipy)2(NO3)]+ complex is six-coordinated, forming a distorted octahedral geometry; bond lengths to the N atoms of the pyridine rings and one of the O atoms of the chelating NO3 ligand lie in the range 1.975u2005(5)–2.139u2005(6)u2005A, with the second O atom from the NO3 ligand less tightly coordinated at a distance of 2.520u2005(6)u2005A. The geometry of the CuN2N′2OO′ chromophore more closely resembles that of [Cu(bipy)2(NO2)]+ complexes than previously reported [Cu(bipy)2(NO3)]+ structures.