AVS 60th International Symposium and Exhibition
    Scanning Probe Microscopy Focus Topic Thursday Sessions
       Session SP+AS+BI+EM+MI+NS+SE+SS-ThA

Invited Paper SP+AS+BI+EM+MI+NS+SE+SS-ThA1
Antibody Movement on Regular Antigen Clusters: Fab Arms are Made for Walking

Thursday, October 31, 2013, 2:00 pm, Room 202 C

Session: Probe-sample Interactions, Nano-manipulation and Emerging Instrument Formats
Presenter: P. Hinterdorfer, Johannes Kepler Univ. & Ctr for Adv. Bioanalysis GmbH, Austria
Authors: J. Preiner, Johannes Kepler Univ. & Ctr for Adv. Bioanalysis GmbH, Austria
N. Kodera, Kanazawa Univ., Japan
J. Tang, Chinese Academy of Sciences
A. Ebner, Johannes Kepler Univ., Austria
M. Brameshuber, Vienna Univ. of Tech., Austria
D. Blaas, Medical Univ. of Vienna, Austria
N. Ilk, Univ. of Natural Resources & Applied Life Sci. Vienna, Austria
H.J. Gruber, Johannes Kepler Univ., Austria
T. Ando, Kanazawa Univ., Japan
P. Hinterdorfer, Johannes Kepler Univ. & Ctr for Adv. Bioanalysis GmbH, Austria
Correspondent: Click to Email
Antibodies are key molecules for the immune system of vertebrates. The Y-shaped IgGs exhibit C2-symmetry; their Fc stem is connected to two identical Fab arms binding antigens. The Fc part is recognized by the complement system and by phagocytic cells. Antibodies can be considered molecular calipers; bivalent binding of the two Fab arms to adjacent antigens can only occur within a distance of roughly 6 to 12 nm. This leads to much higher avidity and slower dissociation rates as compared to monovalent binding. Here we show that antibodies exhibit “bipedal” walking on antigenic surfaces and static binding of both Fab arms of an antibody may hold true only for a time scale of ~ 0.04 s. The walking speed depends on the lateral spacing and symmetry of the antigens. On 2D-crystalline surfaces, such as found on bacteria and viruses, steric strain thus appears to be the main reason for short-lived bivalent binding. Importantly, the collision between randomly walking antibodies was seen to reduce their motional freedom. It leads to formation of transient antibody clusters even at low antibody density. Interestingly, such assemblies are known nucleation sites for docking of the complement system and/or phagocytes.