1. Switching of Bacterial Adhesion to a Glycosylated Surface by
Reversible Reorientation of the Carbohydrate Ligand
Theresa Weber, Vijayanand Chandrasekaran, Insa Stamer, Mikkel B. Thygesen,
Andreas Terfort and Thisbe K. Lindhorst
Department of Biochemistry, Chemistry and Pharmacy; University of Frankfurt(Germany)
Otto Diels Institute of Organic Chemistry; Christiana Albertina University of Kiel(Germany)
CARB Centre, Department of Chemistry; University of Copenhagen (Denmark)
Angew. Chem. Int. Ed. 2014, 53, –14586

2. Cellular adhesion is a surface recognition phenomena
in biological systems by interaction of
carbohydrate-specific proteins (lectins) with
carbohydrate epitopes (ligands) located within the unordered glycoconjugate layer (glycocalyx) of cells.
An important mechanism for the
regulation of bacterial cell adhesion to their host cells depends on the specific binding to the carbohydrates presented at the cell surface, which is mediated by adhesive
organelles of bacteria, called fimbriae.

3. The characterization of these monolayers was
Photoisomerizable glyco-SAMs were fabricated from suitably diluted solutions of synthetic azobenzene mannoside alkanethioacetates.
The characterization of these monolayers was
performed using IRRAS and XPS.
Photoirradiation at appropriate wavelengths led to a characteristic change in the intensity of the prominent band at ~1250 cm-1 containing the Caryl–Oman stretching vibrations. This indicates E→Z conversion of the azobenzene N=N double bond and thus a spatial change of the orientation of the immobilized glycosides on the surface.
V. Chandrasekaran, H. Jacob, F. Petersen, K. Kathirvel, F.
Tuczek, T. K. Lindhorst, Chem. Eur. J. 2014, 20, 8744 – 8752.

4. Adhesion of type 1-fimbriated E
Adhesion of type 1-fimbriated E. coli cells is mediated by the fimbrial protein FimH, a two-domain lectin found at the fimbrial tips.
The orientation-dependent recognition of immobilized α-D-mannoside ligands by FimH determines adhesion of E. coli. To control their orientation, the α-mannoside ligands were attached to solid surfaces in the form of SAMs, which contain photoswitchable azobenzene units.
A short OEG spacer provided a hydrophilic environment and suppressed unspecific surface adhesion. Reversible E/Z photoisomerization was achieved by employing
light of two different wavelengths.

5. IRRA spectra of the azobenzene glycoside monolayer on gold.
During switching, the intensities of many signals vary, with the effect being particularly pronounced for the signals at around 1240 cm-1 (see Inset).
P: pristine SAM,
Z: SAM after irradiation with 365 nm light (2 J cm-2),
E: SAM after irradiation with 450 nm light (100 J cm-2).

6. Adhesion of fluorescent E
Adhesion of fluorescent E. coli cells onto the monolayers (glyco-SAMs) at different irradiation stages:
pristine (= non-irradiated) SAM,
after 1st irradiation with 365 nm (E→Z isomerization),
after 1st irradiation with 450 nm (Z→E isomerization)
after 2nd irradiation with 365 nm,
after 2nd irradiation with 450 nm.
After the respective irradiation step, the samples were incubated in an E. coli suspension for 30 minutes and the area density of bacteria was counted using a fluorescence microscope

7. Bacterial adhesion to an azobenzene
glycoside monolayer on gold through
two E→Z→E isomerization cycles.
The alternating amount of attached E. coli
cells is shown in gray (error bars are 95% confidence intervals), together with the
integral of the prominent IR signal at
1240 cm-1 .
The same alternating trend is visible for both observables indicating that adhesion of bacterial cells is switched with changing orientation of the immobilized carbohydrate ligand

8. Conclusion:
This is the first evidence for an orientation-dependence of a ligand by a biological
system in an interfacial environment without changing the recognition quality of the
ligand itself.
Since the surface of OEG matrix in this present model is similar to the surface of a
glycocalyx, the introduction of an azobenzene unit into the present model system
provides the possibility to induce reorganization by an external stimulus (light)
opening the opportunity to compare binding/recognition events in different states.