The Signal Recognition Particle Receptor of Escherichia coli (FtsY) has a Nucleotide Exchange Factor Built into the GTPase Domain

• Published in: Proceedings of the National Academy of Sciences - PNAS 1997-10, Vol.94 (21), p.11339-11344
• Main Authors: Moser, Claudio, Mol, Olaf, Goody, Roger S., Sinning, Irmgard
• Format: Article
• Language: English
• Subjects: Bacterial Proteins - chemistry; Bacterial Proteins - isolation & purification; Bacterial Proteins - metabolism; Binding Sites; Biological Sciences; Cell biology; Consensus Sequence; Escherichia coli - metabolism; Fluorescence; Gross domestic product; GTP Phosphohydrolases - chemistry; GTP Phosphohydrolases - metabolism; Guanine Nucleotides - metabolism; Guanosine Diphosphate - metabolism; Guanosine Triphosphate - metabolism; Kinetics; Mathematical constants; Nucleotides; Protein Conformation; Proteins; Receptors; Receptors, Cytoplasmic and Nuclear - chemistry; Receptors, Cytoplasmic and Nuclear - isolation & purification; Receptors, Cytoplasmic and Nuclear - metabolism; Recombinant Proteins - chemistry; Recombinant Proteins - isolation & purification; Recombinant Proteins - metabolism; Spectrometry, Fluorescence; Titration; Tryptophan
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.94.21.11339

Targeting of many secretory and membrane proteins to the inner membrane in Escherichia coli is achieved by the signal recognition particle (SRP) and its receptor (FtsY). In E. coli SRP consists of only one polypeptide (Ffh), and a 4.5S RNA. Ffh and FtsY each contain a conserved GTPase domain (G domain) with an α -helical domain on its N terminus (N domain). The nucleotide binding kinetics of the NG domain of the SRP receptor FtsY have been investigated, using different fluorescence techniques. Methods to describe the reaction kinetically are presented. The kinetics of interaction of FtsY with guanine nucleotides are quantitatively different from those of other GTPases. The intrinsic guanine nucleotide dissociation rates of FtsY are about 105times higher than in Ras, but similar to those seen in GTPases in the presence of an exchange factor. Therefore, the data presented here show that the NG domain of FtsY resembles a GTPase--nucleotide exchange factor complex not only in its structure but also kinetically. The I-box, an insertion present in all SRP-type GTPases, is likely to act as an intrinsic exchange factor. From this we conclude that the details of the GTPase cycle of FtsY and presumably other SRP-type GTPases are fundamentally different from those of other GTPases.