Open AccessInvolvement of Laser Photo‐CIDNP(Chemically Induced Dynamic Nuclear Polarization)‐Reactive Amino Acid Side Chains in Ligand Binding by Galactoside‐Specific Lectins in Solution
Author(s) -
Sieber HansChristian,
Adar Rivka,
Arango Rafael,
Burchert Maria,
Kaltner Herbert,
Kayser Gian,
Tajkhorshid Emadeddin,
Lieth ClausWilhelm,
Kaptein Robert,
Sharon Nathan,
Vliegenthart Johannes F. G.,
Gabius HansJoachim
Publication year - 1997
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1997.00027.x
Subject(s) - histidine , galectin , cidnp , chemistry , lectin , side chain , binding site , tryptophan , amino acid , biochemistry , organic chemistry , radical , polymer
For proteins in solution the validity of certain crystallographic parameters can be ascertained by a combination of molecular‐dynamics (MD) simulations and NMR spectroscopy. Using the laser photoCIDNP (chemically induced dynamic nuclear polarization) technique as a measure for surface accessibility of histidine, tyrosine and tryptophan, the spectra of bovine galectin‐1 and Erythrina corallodendron lectin (EcorL) are readily reconcilable with the crystallographic data for these two proteins. The results emphasise the role of Trp68/Trp69 for carbohydrate binding in bovine galectin‐1/chicken galectins and of Trpl94 in murine galectin‐3. This feature derived from the crystal structure of bovine galectin‐1 is maintained in solution for the prototype human homologue, two avian galectins and the chimeratype murine galectin‐3, as the spectra corroborate the CIDNP‐inferable spatial parameters of the four calculated models for binding‐site architecture. In EcorL, Tyr106/Tyr108 are constituents of the extended combining pocket, which can be shielded in solution by ligand presence. Discrepancies between results from modelling and CIDNP measurements concern primarily the lack of reactivity of histidine residues for human and avian prototype galectins and of Tyr82/Tyr229 of the plant lectin. Site‐directed mutagenesis of EcorL is assumed to provide information on the role of a certain residue for functional aspects. When single‐site mutants of EcorL ([Ala106]EcorL, [Ala108]EcorL, [Ala229]EcorL) were subjected to moleculardynamics (MD) simulations, the apparent surface accessibilities even of spatially separated amino acid side chains could non‐uniformly be affected. This conclusion is supported by the assessment of the spectra for the mutant proteins. On the basis of these CIDNP‐results modelling of the binding‐site architecture of the lectin indicates the occurrence of notable alterations in the orientation of Tyr106/Tyr108 phenyl rings. The implied potential effect of single‐site mutations on conformational features of a protein will deserve attention for the interpretation of studies comparing wild‐type and mutant proteins.