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Varied metal-binding properties of lipoprotein PsaA in Streptococcus pneumoniae
Nan Li1, Xiao-Yan Yang, Zhong Guo
1Key Laboratory of Functional Protein Research of Guangdong Higher Education Institutes, Institute of Life and Health Engineering, College of Life Science and Technology, Jinan University, Guangzhou, 510632, China.
Abstract:
Streptococcus pneumoniae is a Gram-positive pathogen responsible for pneumonia, otitis media, and meningitis. Manganese and zinc ions are essential for this bacterium, playing regulatory, structural, or catalytic roles as the critical cofactors in the bacterial proteins and metabolic enzymes. Lipoprotein PsaA has been found to mediate Mn(2+) and Zn(2+) transportation in Streptococcus pneumoniae. In the present work, we conducted a systemic study on the contributions from key amino acids in the metal-binding site of PsaA using various spectroscopic and biochemical methods. Our experimental data indicate that four metal-binding residues contribute unequally to the Mn(2+) and Zn(2+) binding, and His139 is most important for both the structural stability and metal binding of the protein. PsaA-Mn(2+) has a lower thermal stability than PsaA-Zn(2+), possibly due to the different coordination preferences of the metals. Kinetics analysis revealed that PsaA-Mn(2+) binding is a fast first-order reaction, whereas PsaA-Zn(2+) binding is a slow second-order reaction, implying that PsaA kinetically prefers binding Mn(2+) to Zn(2+). The present results provide complementary information for understanding the mechanisms of metal transport and bacterial virulence via lipoproteins in Streptococcus pneumoniae.
Insights
This study reveals how key amino acids in Streptococcus pneumoniae lipoprotein PsaA bind essential manganese (Mn2+) and zinc (Zn2+) ions. His139 is crucial for PsaA stability and metal binding, with PsaA kinetically preferring Mn2+.
Area of Science:
- Microbiology
- Biochemistry
- Structural Biology
Background:
- Streptococcus pneumoniae is a major Gram-positive pathogen causing pneumonia, otitis media, and meningitis.
- Manganese (Mn2+) and zinc (Zn2+) ions are essential cofactors for bacterial proteins and enzymes, crucial for virulence.
- Lipoprotein PsaA facilitates Mn2+ and Zn2+ transport in S. pneumoniae.
Purpose of the Study:
- To investigate the roles of specific amino acids in the metal-binding site of PsaA.
- To elucidate the differential contributions of these residues to Mn2+ and Zn2+ binding.
- To understand the impact of metal binding on PsaA stability and kinetics.
Main Methods:
- Spectroscopic techniques
- Biochemical assays
- Kinetic analysis
Main Results:
- Four metal-binding residues contribute unequally to Mn2+ and Zn2+ binding.
- Histidine 139 (His139) is critical for PsaA structural stability and metal ion coordination.
- PsaA-Mn2+ exhibits lower thermal stability than PsaA-Zn2+.
- PsaA-Mn2+ binding is a fast first-order reaction, while PsaA-Zn2+ binding is a slow second-order reaction, indicating a kinetic preference for Mn2+.
Conclusions:
- The study provides detailed insights into the metal-binding mechanisms of PsaA.
- Differential metal binding and stability influence bacterial virulence.
- Findings contribute to understanding metal ion transport and pathogenesis in S. pneumoniae.
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