Life science
Healthcare

Elucidation of the molecular basis of cell adhesion to thebasement membrane
Division of Protein Chemistry, Institute for Protein Research
Professor Junichi Takagi

Researchmap https://researchmap.jp/read0105692

Associate Professor Takao Arimori

Researchmap https://researchmap.jp/t_arimoriLife science

Abstract
Laminins are major component of basement membranes andbind to integrins, cell surface receptors, to attach epithelial cells tothe basement membranes (Fig. 1). The binding between laminin
and integrin plays important roles in embryonic development, organ formation and homeostasis. We have succeeded in determining the solitary crystal structure of integrin α6β1 and the cryo-EMstructure of the integrin α6β1-laminin 511 complex by utilizing of
our original Fv-clasp technology (Fig. 2). These structures revealed
how integrin recognizes laminin and how integrin transmits signals
into the cell.

ciently cultivate these cells. Our findings will greatly help in thedevelopment of better culture substrates and contribute to the fieldof regenerative medicine.

▍ Background & Results
The surfaces of various organs are composed of epithelial cells
attached to a sheet-like structure called basement membrane. Cell
adhesion to the basement membrane and the associated signaltransduction are essential processes for the normal functioning ofeach organ. Laminins, major component of the basement membranes, and their receptor integrins play a central role in cell adhesion (Fig. 1). However, the structural analysis of both laminins
and integrins is very difficult due to their size and flexibility, and thedetails of their recognition mechanisms remain unknown.
Small antibody fragments including Fab and single-chain Fv
are often used as tools to facilitate structural analysis, because
the binding of antibody fragments usually stabilize the structure oftarget molecules. However, conventional small antibodies sometimes exhibit problems in their productivity and structural rigidity.
Therefore, we have previously developed a novel small antibody
fragment format "Fv-clasp" that overcomes these problems. In thisstudy, we succeeded in obtaining important structural information
for laminin/integrin by applying Fv-clasp to their structural analysis.
In the crystallization of integrin α6β1, crystals were obtained forthe first time by using Fv-clasp as a crystallization chaperone, andthe structure could be determined (Fig. 2, left). In addition, for thecomplex of integrin α6β1 and its ligand laminin 511, a very stablecomplex was obtained in the presence of Fv-clasp, making it possible to determine its structure by cryo-EM single particle analysis(Fig. 2, right). From these structures, we were able to visualize alarge conformational change of integrin upon laminin binding. Furthermore, it revealed that the interaction between the C-terminal
region of the laminin γ chain and integrin was accompanied by alocal conformational change, which triggered the overall conformational change. Those structural observation clarified the molecularmechanism of integrin-mediated signal transduction in detail.

Fig. 1 Adhesion of epithelial cells to basement membranes
主要図（英語版）

laminin 511
Fv-clasp

Fv-clasp

integrin α6integrin β1

integrin α6integrin β1

Fv-clasp

Fig. 2 Fig.
Crystalstructureof the integrin(left) andcryo-EM
structure of the2 Crystal
structureof the integrin(left)and cryo-EM
α6β1 α6β1structureof the integrin
α6β1-laminin
integrin
511 complex(right) 511 complex (right)
α6β1-laminin▍ Significance of the research and Future perspective

It is known that integrin α6β1 is abundant on the surface ofpluripotent stem cells, such as ES cells and iPS cells, and laminin
511 has already been widely used as a culture substrate to effi-

P a t e n t
Arimori, T et al. Fv-clasp: An artificially designed small antibody fragment with improved production compatibility, stability, and crystallizability. Structure.
T r e a t i s e 2017; 25(10): 1611-1622. doi: 10.1016/j.str.2017.08.011
Arimori, T et al. Structural mechanism of laminin recognition by integrin. Nat. Commun. 2021; 12 (1): 4012. doi: 10.1038/s41467-021-24184-8
URL
K e y w o r d cell adhesion, pluripotent stem cell, small antibody fragment