Staphylococcal biofilm-forming protein has a contiguous rod-like structure

Area of Science:

• Microbiology and Structural Biology
• Biochemistry and Biophysics

Background:

• Staphylococcus aureus and Staphylococcus epidermidis form antibiotic-resistant biofilms on medical devices, causing significant patient morbidity and mortality.
• Current treatment often requires device removal, highlighting the need for new therapeutic strategies and molecular understanding.
• Surface proteins like SasG and accumulation-associated protein are known to promote biofilm formation via their 'B' regions.

Purpose of the Study:

• To elucidate the structural and biophysical mechanisms underlying Staphylococcus biofilm formation.
• To investigate the role of 'E' and 'G5' domains in the 'B' regions of surface proteins.
• To determine the proposed Zn(2+)-mediated homodimerization in intercellular accumulation.

Main Methods:

• Determined the structures of E-G5 and G5-E-G5 fragments from Staphylococcus aureus surface protein G (SasG).
• Characterized the biophysical properties of single and multi-domain fragments.
• Assessed the effect of Zn(2+) on SasG domain dimerization.

Main Results:

• E sequences cooperatively fold and interlock with G5 domains, forming elongated, contiguous, monomeric structures.
• G5 domains and multi-domain constructs exhibit significant thermodynamic stability despite lacking a compact hydrophobic core.
• Zn(2+) was found not to induce dimerization of SasG domains, challenging the proposed 'zinc zipper' mechanism.

Conclusions:

• The study reveals a novel paradigm for the formation of bacterial fibrils on the 100-nm scale.
• Bacterial biofilm accumulation likely occurs through a mechanism distinct from Zn(2+)-mediated homodimerization.
• The unique domain arrangement in proteins like SasG may reduce misfolding in tandem repeat sequences.