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Expression, purification, crystallization and preliminary crystallographic analysis of SpaA, a major pilin from
Hae Joo Kang1, Neil G Paterson, Edward N Baker
1School of Biological Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand.
Abstract:
Bacterial pili are cell-surface organelles that are critically involved in adhesion to host cells, leading to the colonization of host tissues and the establishment of infections. Whereas the pili of Gram-negative bacteria have been extensively studied, those of Gram-positive bacteria came to light only recently after the discovery and characterization of Corynebacterium diphtheriae pili. These newly discovered pili are formed by the covalent polymerization of pilin subunits catalyzed by sortase enzymes, making them fundamentally different from the noncovalent pilin assemblies of Gram-negative bacteria. Here, the expression, crystallization and preliminary crystallographic analysis of SpaA, which forms the shaft of one of the three types of pili expressed by C. diphtheriae, are reported. SpaA(53-486) crystals diffracted to 1.6 A resolution and belonged to space group P2(1)2(1)2(1), with unit-cell parameters a = 34.9, b = 64.1, c = 198.7 A, alpha = beta = gamma = 90 degrees .
Insights
Researchers characterized pili from Corynebacterium diphtheriae, revealing distinct covalent assembly mechanisms in Gram-positive bacteria. This study focused on SpaA pilin structure, crucial for understanding bacterial adhesion and infection.
Area of Science:
- Microbiology
- Structural Biology
- Biochemistry
Background:
- Bacterial pili are vital for host cell adhesion, tissue colonization, and infection establishment.
- Gram-negative bacterial pili are well-studied, but Gram-positive bacterial pili, like those of Corynebacterium diphtheriae, have only recently been discovered.
- Unlike Gram-negative pili, Gram-positive pili are covalently polymerized by sortase enzymes.
Purpose of the Study:
- To report the expression, crystallization, and preliminary crystallographic analysis of SpaA, a pilin subunit forming the shaft of Corynebacterium diphtheriae pili.
- To provide structural insights into Gram-positive bacterial pili assembly.
Main Methods:
- Expression of the SpaA pilin subunit (SpaA(53-486)).
- Crystallization of the SpaA protein.
- Preliminary X-ray crystallographic analysis of SpaA crystals.
Main Results:
- SpaA(53-486) crystals were obtained and diffracted to 1.6 Å resolution.
- The crystals belonged to space group P2(1)2(1)2(1).
- Unit-cell parameters were determined: a = 34.9 Å, b = 64.1 Å, c = 198.7 Å, with α = β = γ = 90°.
Conclusions:
- The study provides initial structural data for SpaA, a key component of Gram-positive bacterial pili.
- This work lays the foundation for understanding the unique covalent assembly mechanism of Gram-positive pili.
- The structural information will aid in developing strategies targeting bacterial adhesion and infection.
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