More affinity than for what?

Try to look into these papers:

Lei HY and Chang CP (2009) Lectin of Concanavalin A as an Anti-Hepatoma Therapeutic Agent. J. Biomed. Sci. 16:10;

Komath SS, Kavitha M, Swamy MJ (2006) Beyond Carbohydrate Binding: New Directions in Plant Lectin Research. Org. Biomol. Chem. 4, 973-988;

Maybe you will find your answer there.

i'll look the papers that you recomend me, thanks for that, what I am trying to understand is the interacion between the lectins and the glucoside groups in this case Concanavalin-A and α-mannosyl.

thanks againg

ConA binds Man better than Glc because it was probably designed by evolution to bind to the core of high-Man (i.e. non-complex) N-glycans and be toxic (plant vs plant eater). Which structural component (could be just one amino acid or a whole chain) in the sugar binding part of ConA would have to be changed to better bind Glc than Man is beyond me, I very much doubt that's been looked at by sane persons. Here's a list of toxic lectins binding to different sugar structures: http://stanxterm.aecom.yu.edu/secondary/lec.htm . You'll find that the less complex the N-glycans are, the better they bind ConA (i.e. the more sensitive cells get to exposure with the lectin). Which of the aminoacids are interacting with the -OH group in Man that's different to Glc (2 or 5?) could conceivably be found in a structural (X-ray) paper since ConA can be purified well but I haven't found anything on the quick in pubmed. I don't know how they'd behave in a column but that you should find in literature (there's a book that I could find if you absolutely needed that info). I will hazard a guess that ConA has good affinities to aGlc, because lectins very often bind to different -OH groups simultaneously. If you are looking for biological significance, think in whole (sugar-) structures. What's the experiment that you want to do?

Hi I am purifing a protein from the basolateral membrane of kidney cell and one step is during the purification is doing an affinity chromatography so the Na/Katpase that have a high manose residue on the glycoprotein subunit stay in the column and the first eluate is the one with my protein of interest, but I am interest in know how come that happens, why differents lectins have different affinities for differents sugars

A lectin is any protein that binds sugars. This class of proteins is extremely divers in both function and structure and has evolved from different sources for different purposes thus there is no non-trivial answer to your question. I hope that this purification step you are talking about has been done before and is worth doing, in which case you should adhere religiously (incl. protein concentrations and amounts/column - don't try to up- or downscale) to the protocol because it's bound to be fickle. And it's a membrane protein that is solubilized with a detergent making micelles(?) that are containing all sorts of (glycan decorated!) proteins. And it's big so you have probably gel filtration effects in there if the ConA is bound to Sepharose... If you have just invented this ConA purification step yourself, I'd advice against it and use - if you must use lectins - a Gal , GlcNAc or Sia binding one (WGA or so) to positively purify complex N-glycan decorated proteins. Well ... good luck and welcome to Glycobiology - science of the brave.

The best classification of lectin is based in its structure nor in its affinity, but usually lectins evolutionarily related have primary and tridimensional structures with high similarity, and almost all carbohydrate binding sites have the same residues and similar orientation, those features ensure the same recognition for related lectins as Legume (as ConA, ConBr, ConM, ConGf, DGL, Dgui, DVL, etc) lectins that are Glucose/Mannose binding lectins. The recognition is specific and depends mostly on hydrogen bonds between residues in the carbohydrate recognition domain (CRD) and hydroxyl groups from carbohydrates. I'll give you some examples of how interaction occurs, if we take legume lectins, the affinity for mannose is higher than glucose, the reason of this is the different orientation of one hydroxyl of mannose that increases the number of hydrogen bonds and consequently the affinity for this sugar, we also have in the CRD weaker interactions like van der Walls tha are present, other modifications as methylations in the sugar can increase affinity, because in the CRD of those lectins there is a hydrophobic sub-site that accommodate the methyl group increasing the number of interactions and affinity.

The conformation of carbohydrates different from glucose and mannose (and their derivatives) can't perform optimal interactions that favor the recognition in legume lectins.

I hope that this explanation can help you with your questions.