Mutating conserved cysteines in the alphavirus e2 glycoprotein causes virus-specific assembly defects.

Area of Science:

• Virology
• Molecular Biology
• Structural Biology

Background:

• Alphavirus surface spikes, composed of E2 and E1 glycoproteins, mediate viral entry and interact with the nucleocapsid.
• The E2 glycoprotein is crucial for receptor binding, membrane fusion, and particle assembly, with its function potentially altered by mutations.
• E2 is a conserved, cysteine-rich transmembrane glycoprotein essential for alphavirus infectivity.

Purpose of the Study:

• To investigate the functional impact of cysteine mutations in the E2 ectodomain of alphaviruses.
• To determine how E2 mutations affect virus entry, spike assembly, and maturation in different alphavirus species.

Main Methods:

• Generated single cysteine-to-serine mutations in two distinct regions of the E2 ectodomain in Sindbis virus and Ross River virus.
• Assessed the infectivity of mutant viruses compared to wild-type.
• Characterized differences in particle morphology, fusion activity, and polyprotein cleavage between mutant viruses.

Main Results:

• All E2 cysteine mutants produced fewer infectious particles than wild-type viruses.
• Mutant viruses exhibited variations in particle morphology and fusion activity.
• Significant differences in polyprotein cleavage and assembly defects were observed between Sindbis and Ross River virus mutants, despite conserved mutation sites.

Conclusions:

• Cysteine residues in the E2 ectodomain are critical for alphavirus infectivity.
• E2 glycoprotein function and folding are species-dependent, likely influenced by virus-specific chaperones.
• The observed nonconserved assembly defects highlight the intricate, species-specific nature of alphavirus E2 glycoprotein interactions.