Giardia gene predicts a 183 kDa nucleotide-binding head-stalk protein

Area of Science:

• Cell Biology
• Structural Biology
• Parasitology

Background:

• Giardia lamblia cytoskeleton proteins, such as beta-giardin and median body protein, exhibit segmented coiled-coil structures with regular repeat patterns.
• Previous studies identified these proteins as key components of the parasite's cytoskeleton.

Purpose of the Study:

• To identify and characterize novel cytoskeleton proteins in Giardia lamblia.
• To determine the structural and functional properties of a newly identified large polypeptide chain, HPSR2.

Main Methods:

• Screening of a Giardia genomic DNA library using antibodies against a giardin isoform.
• Gene cloning, sequencing via chromosome walking, and expression of the HPSR2 gene as a recombinant protein.
• Bioinformatic analysis of the predicted amino acid sequence, including Fourier analysis of the stalk region.

Main Results:

• A gene encoding a large polypeptide chain (HPSR2) was isolated and characterized.
• The recombinant HPSR2 protein has a molecular mass of 183 kDa.
• Sequence analysis predicts a motor protein with an N-terminal hydrolytic domain and a long coiled-coil stalk composed of repeating heptad units, similar to myosin and kinesin.
• Fourier analysis revealed a strong physical repeat in the stalk, with segments of 25 residues, resembling the median body protein's 24-residue segments.

Conclusions:

• HPSR2 represents a novel motor protein in Giardia lamblia with a distinct segmented coiled-coil structure.
• The structural features suggest a potential role in cytoskeletal organization or movement within the parasite.
• The findings contribute to understanding the molecular architecture and function of the Giardia cytoskeleton.