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X-Ray Reflectivity and Grazing Incidence Diffraction Studies of Interaction between Human Adhesion/Growth-Regulatory Galectin-1 and DPPE–GM1 Lipid Monolayer at an Air/Water Interface

J. Majewski1, S. André2, E. Jones3, E. Chi3, and H.-J. Gabius2*

1Manuel Lujan Jr. Neutron Scattering Center, Los Alamos Neutron Science Center, Los Alamos National Laboratory, Los Alamos, NM, USA

2Institute of Physiological Chemistry, Faculty of Veterinary Medicine, Ludwig-Maximilians-University Munich, Veterinärstr. 13, 80539 München, Germany; E-mail: gabius@tiph.vetmed.uni-muenchen.de; gabius@lectins.de

3Department of Chemical and Biological Engineering, Center for Biomedical Engineering, University of New Mexico, Albuquerque, NM, USA

* To whom correspondence should be addressed.

Received October 26, 2014; Revision received April 14, 2015
The specific interaction of ganglioside GM1 with the homodimeric (prototype) endogenous lectin galectin-1 triggers growth regulation in tumor and activated effector T cells. This proven biorelevance directed interest to studying association of the lectin to a model surface, i.e. a 1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine/ganglioside GM1 (80 : 20 mol%) monolayer, at a bioeffective concentration. Surface expansion by the lectin insertion was detected at a surface pressure of 20 mN/m. On combining the methods of grazing incidence X-ray diffraction and X-ray reflectivity, a transient decrease in lipid-ordered phase of the monolayer was observed. The measured electron density distribution indicated that galectin-1 is oriented with its long axis in the surface plane, ideal for cis-crosslinking. The data reveal a conspicuous difference to the way the pentameric lectin part of the cholera toxin, another GM1-specific lectin, is bound to the monolayer. They also encourage further efforts to monitor effects of structurally different members of the galectin family such as the functionally antagonistic chimera-type galectin-3.
KEY WORDS: agglutinin, Bragg peaks, ganglioside, lectin, X-ray diffraction/reflectivity

DOI: 10.1134/S0006297915070135