Structural and functional similarity between the bacterial type III secretion system needle protein PrgI and the eukaryotic apoptosis Bcl-2 proteins

• Published in: PloS one 2009-10, Vol.4 (10), p.e7442-e7442
• Main Authors: Shortridge, Matthew D, Powers, Robert
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Amino acids; Analysis; Apoptosis; Bacteria; Bacterial Proteins - chemistry; Bacterial Proteins - physiology; Bcl-2 protein; Bcl-x protein; bcl-X Protein - metabolism; Benzophenanthridines - pharmacology; Binding sites; Biochemistry; Biochemistry/Bioinformatics; Biochemistry/Biomacromolecule-Ligand Interactions; Biochemistry/Drug Discovery; Biochemistry/Experimental Biophysical Methods; Biochemistry/Molecular Evolution; Biochemistry/Structural Genomics; Biophysics/Biomacromolecule-Ligand Interactions; Biophysics/Experimental Biophysical Methods; Biophysics/Structural Genomics; Carrier Proteins - chemistry; Carrier Proteins - physiology; Catalytic Domain; Cell death; Cell growth; Chelerythrine; Computational Biology - methods; Conservation; Conserved sequence; Humans; Infections; Interfaces; Ligands; Magnetic Resonance Spectroscopy; Molecular Sequence Data; NMR; Nuclear magnetic resonance; Nucleotide sequence; Oligomerization; Oligomers; Pore formation; Protein Binding; Protein structure; Proteins; Proto-Oncogene Proteins c-bcl-2 - metabolism; Salmonella; Salmonella typhimurium; Salmonella typhimurium - metabolism; Secretion; Sequence Homology, Amino Acid; Similarity; Software; Structural analysis; Structure-function relationships
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0007442

Functional similarity is challenging to identify when global sequence and structure similarity is low. Active-sites or functionally relevant regions are evolutionarily more stable relative to the remainder of a protein structure and provide an alternative means to identify potential functional similarity between proteins. We recently developed the FAST-NMR methodology to discover biochemical functions or functional hypotheses of proteins of unknown function by experimentally identifying ligand binding sites. FAST-NMR utilizes our CPASS software and database to assign a function based on a similarity in the structure and sequence of ligand binding sites between proteins of known and unknown function. The PrgI protein from Salmonella typhimurium forms the needle complex in the type III secretion system (T3SS). A FAST-NMR screen identified a similarity between the ligand binding sites of PrgI and the Bcl-2 apoptosis protein Bcl-xL. These ligand binding sites correlate with known protein-protein binding interfaces required for oligomerization. Both proteins form membrane pores through this oligomerization to release effector proteins to stimulate cell death. Structural analysis indicates an overlap between the PrgI structure and the pore forming motif of Bcl-xL. A sequence alignment indicates conservation between the PrgI and Bcl-xL ligand binding sites and pore formation regions. This active-site similarity was then used to verify that chelerythrine, a known Bcl-xL inhibitor, also binds PrgI. A structural and functional relationship between the bacterial T3SS and eukaryotic apoptosis was identified using our FAST-NMR ligand affinity screen in combination with a bioinformatic analysis based on our CPASS program. A similarity between PrgI and Bcl-xL is not readily apparent using traditional global sequence and structure analysis, but was only identified because of conservation in ligand binding sites. These results demonstrate the unique opportunity that ligand-binding sites provide for the identification of functional relationships when global sequence and structural information is limited.