A new mechanism of fibronectin fibril assembly revealed by live imaging and super-resolution microscopy

Abstract

AbstractFn1 fibrils have long been viewed as continuous fibers composed of extended, periodically aligned Fn1 molecules. However, our live imaging and single-molecule localization microscopy (SMLM) are inconsistent with this traditional view and show that Fn1 fibrils are composed of roughly spherical nanodomains containing 6-11 Fn1 dimers. As they move toward the cell center, Fn1 nanodomains become organized into linear arrays, wherein nanodomains are spaced at the average periodicity of 105±17 nm. Periodical Fn1 nanodomain arrays are bona fide fibrils: they are resistant to deoxycholate treatment and retain nanodomain periodicity in the absence of cells. The nanodomain periodicity in fibrils remained constant when probed with antibodies recognizing distinct Fn1 epitopes or combinations of antibodies recognizing epitopes spanning the length of Fn1. FUD, a bacterial peptide that binds Fn1 N-terminus and disrupts Fn1 fibrillogenesis does not disrupt the formation of Fn1 nanodomains, instead, it blocks the organization of Fn1 nanodomains into periodical arrays. These studies establish a new paradigm of Fn1 fibrillogenesis.