Concanavalin crystal structure

Fig. 4. Backscattered Raman and ROA spectra of the n-helical protein human serum albumin in H20 (top pair) and the /3-sheet protein jack bean concanavalin A in acetate buffer solution at pH 5.4, together with MOLSCRIPT diagrams (Kraulis, 1991) of their X-ray crystal structures (PDB codes lao6 and 2cna). 

Figure 13.2 The crystal structures of (a) concanavalin A and (b) the carbohydrate recognition domain of galectin-3. Residues in the carbohydrate binding sites are black.

Mn is an essential element and occurs in a number of enzymes and is also known to stimulate enzymic activity by reversible association. ESR and NMR line broadening are particularly useful techniques for studying Mn" environments in proteins.148 These measurements and crystal structure studies (concanavalin, Table 11) suggest near regular octahedral coordination by O and N donors. 

Figure 1 The main chain of concanavalin A as determined by X-ray crystal structure analysis. The homotetramer and monomeric subunits are shown with bound ligand.

A listing of the X-ray crystal structure (arranged in chronological order) of plant lectins is presented in Table 2 commencing with the structure of concanavalin A at 3 A resolution [38,39]. Interestingly, it was not until 1989 that a definitive high resolution X-ray crystal structure of the concanavalin A-methyl a-D-mannopyranoside complex was elucidated [40], and the most recently reported is that of peanut agglutinin [41]. Reviews on carbohydrate-protein interactions are also worthy of note [42-45]. 

Without doubt, concanavalin A (Con A) is the most celebrated and has proven to be one of the most useful of the plant lectins. Its physical chemical properties and carbohydratebinding properties are well documented in previous reviews [3,8]. Suffice it to note that it was first isolated and crystallized by Sumner and Howell in 1936, who showed it to require metal ions for its activity [74]. By virtue of its interaction with branched a-D-glucans, it is readily prepared by affinity chromatography on crossed-linked dextran (Sephadex) [75, 76]. A homotetramer at pH 7 (subunit M, = 26 500 Da) of Con A has been sequenced [77] and its crystal structure determined both in its native form [38,39] and complexed with methyl a-D-mannopyranoside [40] and Man(al-3)[Man(al-6)]Man[49]. 

The crystal structure of demetallized concanavalin A has been determined, at a resolution of 3.2Observed differences between the native and demetallized proteins have formed the basis for a mechanistic model of the interactions in solution between the two metal-binding sites. Intact sub-units of concanavalin A have been isolated after ion-exchange chromatography of the lectin in the presence of H4-edta. ... 

Lin, S.-L., Stern, E. A., Kalb (Gilboa), A. J., and Zhang, Y. (1990). Evidence from X-ray absorption fine structure spectroscopy for significant differences in the structure of concanavalin A in solution and in the crystal. Biochemistry, 29, 3599-3603. 

The work on Concanavalin A (Con A) has elegantly illustrated that NMR methods on solutions can be used to obtain structural data complementary to that from X-ray methods on crystals. Con A monomers (mol. wt. 26000) contain one Ca and one Mn ion and bind one sugar molecule (a-D-gluco- or a-D-mannopyranosides). Brewer, Sternlicht, Marcus and Grollman [45,46] concluded from C NMR that the distance between the Mn " ion and a bound glucopyranoside sugar (7) is about 10 A, which contrasts with the X-ray finding of 20 A. This prompted... 

The spreading-out of a protein on an affinity matrix at a critically low density, below which intermolecular bridge formation does not occur, prior to reaction with a chemical cross-linker e.g., glutaraldehyde) has provided an approach which has yielded valuable information about the tertiary and quaternary structure of concanavalin A. Results were in agreement with evidence available from crystallography and other chemico- and bio-physical techniques. This matrix approach promises to be particularly useful in the structural study of poorly soluble membrane-bound proteins and other proteins which are difficult to crystallize. 

The best known plant L. are Concanavalin A (Con A) from jack beans (Canavalia ensifornus), which was crystallized in 1919 by Sumner, and the agglutinins from wheat germ (WGA), lima beans, green beans (Phaseolus), castor beans Ricinus) and potatoes. WGA is very well characterized, and L. with similar specificities and structure are present in rye and barley. Seeds from 90 other members of the Triticeae tribe of... 

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