Abstract
The pneumococcal serine rich repeat protein (PsrP) is displayed on the surface of Streptococcus pneumoniae with a suggested role in colonization in the human upper respiratory tract. Full-length PsrP is a 4000 residue-long multi-domain protein comprising a positively charged functional binding region (BR) domain for interaction with keratin and extracellular DNA during pneumococcal adhesion and biofilm formation, respectively. The previously determined crystal structure of the BR domain revealed a flat compressed barrel comprising two sides with an extended β-sheet on one side, and another β-sheet that is distorted by loops and β-turns on the other side. Crystallographic B-factors indicated a relatively high mobility of loop regions that were hypothesized to be important for binding. Furthermore, the crystal structure revealed an inter-molecular β-sheet formed between edge strands of two symmetry-related molecules, which could promote bacterial aggregation during biofilm formation. Here we report the near complete 15N/13C/1H backbone resonance assignment of the BR domain of PsrP, revealing a secondary structure profile that is almost identical to the X-ray structure. Dynamic 15N-T1, T2 and NOE data suggest a monomeric and rigid structure of BR with disordered residues only at the N- and C-termini. The presented peak assignment will allow us to identify BR residues that are crucial for ligand binding.
Highlights
The Gram-positive commensal and human-adapted bacterium Streptococcus pneumoniae colonizes the upper respiratory tract in about 10% of healthy adults and up to 60% of children, without necessarily causing any symptoms
For efficient colonization within the nasopharynx, pneumococcus displays a multitude of surface-exposed modular adhesive and catalytic proteins (Perez-Dorado et al 2012). One such adhesin is the giant pneumococcal serine rich repeat protein (PsrP), that was discovered as a key colonization factor present in 60% of pneumococcal strains capable of causing pneumonia in children (Blanchette-Cain et al 2013; Sanchez et al 2010)
Their functional binding region (BR) domains, which bind to a broad range of targets including extracellular DNA, glyco-conjugates and keratins, are variable in sequence and organized into modular domains (Lizcano et al 2012)
Summary
The Gram-positive commensal and human-adapted bacterium Streptococcus pneumoniae colonizes the upper respiratory tract in about 10% of healthy adults and up to 60% of children, without necessarily causing any symptoms (van der Poll and Opal 2009). Keywords NMR assignments · Pneumococcal serine rich repeat protein · Secondary structure · X-ray comparison · Backbone dynamics The positively charged BR domain of PsrP binds to negatively charged helical structures such as keratin-10 (KRT-10) and eDNA, possibly to promote efficient bacterial attachment to the upper respiratory tract and during biofilm formation, respectively (Sanchez et al 2010; Shivshankar et al 2009; Blanchette-Cain et al 2013; Schulte et al 2014, 2016).
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