Structure and function of an atypical homodimeric actin capping protein from the malaria parasite

Area of Science:

• Parasitology
• Molecular Biology
• Structural Biology

Background:

• Apicomplexan parasites like Plasmodium rely on the glideosome, an actomyosin motor, for motility and host cell invasion.
• Actin filament dynamics are crucial for parasite life cycle stages and are regulated by actin filament capping proteins (CPs).
• The precise role and mechanism of CPs in Apicomplexa remain largely unknown, particularly compared to well-characterized eukaryotic CPs.

Purpose of the Study:

• To present the first crystal structure of a homodimeric CP from Plasmodium berghei (PbCP).
• To compare the structures of homo- and heterodimeric PbCPs and elucidate their distinct functional mechanisms.
• To investigate the atypical regulation of actin dynamics by PbCPs in the malaria parasite.

Main Methods:

• X-ray crystallography to determine the structure of homodimeric PbCP.
• Biochemical assays to analyze actin dynamics regulation by homo- and heterodimeric PbCPs.
• Structural comparison of homodimeric PbCP with known heterodimeric CPs.

Main Results:

• The crystal structure of homodimeric PbCP revealed unique features distinguishing it from canonical heterodimeric CPs.
• Both homo- and heterodimeric PbCPs regulate actin dynamics atypically, promoting rapid actin turnover without altering critical concentration.
• Homodimeric PbCP may recruit lateral actin dimers, suggesting a novel binding mode due to the absence of a β-subunit.

Conclusions:

• Homodimeric PbCP plays a critical role in regulating malaria parasite actin dynamics through a potentially novel mechanism.
• Redundant activities between homo- and heterodimeric PbCPs may ensure actin filament capping across different parasite life stages.
• Understanding these unique CP structures and functions is vital for developing new anti-malarial strategies targeting parasite motility and invasion.