Abstract
Functional amyloids have been identified in a wide range of organisms, taking on a variety of biological roles and being controlled by remarkable mechanisms of directed assembly. Here, we report that amyloid fibrils constitute the ribs of the buoyancy organelles of Anabaena flos-aquae. The walls of these gas-filled vesicles are known to comprise a single protein, GvpA, arranged in a low pitch helix. However, the tertiary and quaternary structures have been elusive. Using solid-state NMR correlation spectroscopy we find detailed evidence for an extended cross-β structure. This amyloid assembly helps to account for the strength and amphiphilic properties of the vesicle wall. Buoyancy organelles thus dramatically extend the scope of known functional amyloids.
Highlights
The gas vesicles of aquatic microorganisms are hollow proteinaceous shells with remarkable physical properties that enable them to function as floatation organelles
We report that amyloid fibrils constitute the ribs of the buoyancy organelles of Anabaena flos-aquae
Having previously assigned 80% of the gas vesicle protein A (GvpA) resonances in uniformly 13C- and 15N-labeled gas vesicles of A. flos-aquae [14], we sought to validate our model by checking for the predicted interactions between -strands in long range correlation spectra
Summary
The gas vesicles of aquatic microorganisms are hollow proteinaceous shells with remarkable physical properties that enable them to function as floatation organelles. We report that amyloid fibrils constitute the ribs of the buoyancy organelles of Anabaena flos-aquae The walls of these gas-filled vesicles are known to comprise a single protein, GvpA, arranged in a low pitch helix. The model was initially developed based on the secondary structure propensity of the sequence, the positions of conserved residues among different organisms, electrostatic energy considerations, and the x-ray determined tilt of the -strands relative to the vesicle axis [13]. In this model, GvpA monomers contain a -hairpin that forms an antiparallel -sheet within the monomer. Previous solid-state nuclear magnetic resonance (NMR) studies have provided support for the secondary structures inherent in the model: the asymmetric dimer repeat unit is con-
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