Figure 3.
Figure 3. The SR linker is important for efficient SRP-SR assembly during their reciprocally activated GTPase cycle. (A) Reaction scheme depicting the GTPase cycle of SRP and SR. SRP and SR are loaded with GTP before their assembly (GTPSRP+SRGTP). As GTP hydrolysis (kcat) is much faster than SRP⋅SR complex dissociation (Peluso et al., 2001; Lee et al., 2018), SRP-SR association is rate limiting for kcat/Km at subsaturating SR concentrations (Fersht, 1999). The complex dissociates once GTP is hydrolyzed, releasing free SRP and SR to initiate a new round of the GTPase cycle. (B–D) Representative SR concentration dependences of the reciprocally stimulated GTPase reactions between SRP and SR for WT SR and indicated SR mutants (B). The lines are fits of the data to Eq. 3 in Materials and methods, and the obtained kcat/Km and kcat values are reported in C and D, respectively. All values are reported as mean ± SD, with n ≥ 2.

The SR linker is important for efficient SRP-SR assembly during their reciprocally activated GTPase cycle. (A) Reaction scheme depicting the GTPase cycle of SRP and SR. SRP and SR are loaded with GTP before their assembly (GTPSRP+SRGTP). As GTP hydrolysis (kcat) is much faster than SRP⋅SR complex dissociation (Peluso et al., 2001; Lee et al., 2018), SRP-SR association is rate limiting for kcat/Km at subsaturating SR concentrations (Fersht, 1999). The complex dissociates once GTP is hydrolyzed, releasing free SRP and SR to initiate a new round of the GTPase cycle. (B–D) Representative SR concentration dependences of the reciprocally stimulated GTPase reactions between SRP and SR for WT SR and indicated SR mutants (B). The lines are fits of the data to Eq. 3 in Materials and methods, and the obtained kcat/Km and kcat values are reported in C and D, respectively. All values are reported as mean ± SD, with n ≥ 2.

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