How does changing Trp105 to alanine affect the ability of CEL-I to interact with

Question

How does changing Trp105 to alanine affect the ability of CEL-I to interact with GaINAc?

CEL-I is a C -type lectin, purified from the sea cucumber Cucumaria echinata, that shows a high specificity for N-acetylgalactosamine (GaINAc). Lectins are proteins that interact with carbohydrates. An X-ray crystallographic image of GaINAc interacting with specific amino acids of CEL-I is shown below (Sugawara, H. et al. J. Biol. Chem. 2004;279:45219-45225, used by permission). [NOTE: Two different X-ray crystallographic images showing slightly different configurations are overlaid in the image below.]

Explanation / Answer

Answer:

In the case of CEL-I, the binding of GalNAc is stabilized by Trp-105 located near the C6 atom of GalNAc.

the Trp105 residues in all protomers make van der Waals contact with the C-6 atom of GalNAc, thereby stabilizing the binding of GalNAc.

Tryptophan residues have been found to stabilize the binding of carbohydrates in the Gal/GalNAc-recognizing C-type CRDs.

However, the interaction between Trp105 and the C-6 atom of GalNAc appears to be relatively weak in the case of CEL-I in the GalNAc-binding mutant (due to replacement of alanine ) of Mannose-binding protein (MBP), which makes van der Waals contacts with the C-3, C-4, C-5, and C-6 carbon atoms of GalNAc .

so, the replacement of the Trp-105 with alanine makes the weak vanderwaals contacts, due to muattion.

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