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Crystal structure analysis reveals a spring-loaded latch as molecular mechanism for GDF-5-type I receptor specificity.

ABSTRACT: Dysregulation of growth and differentiation factor 5 (GDF-5) signalling, a member of the TGF-beta superfamily, is strongly linked to skeletal malformation. GDF-5-mediated signal transduction involves both BMP type I receptors, BMPR-IA and BMPR-IB. However, mutations in either GDF-5 or BMPR-IB lead to similar phenotypes, indicating that in chondrogenesis GDF-5 signalling seems to be exclusively mediated through BMPR-IB. Here, we present structural insights into the GDF-5:BMPR-IB complex revealing how binding specificity for BMPR-IB is generated on a molecular level. In BMPR-IB, a loop within the ligand-binding epitope functions similar to a latch allowing high-affinity binding of GDF-5. In BMPR-IA, this latch is in a closed conformation leading to steric repulsion. The new structural data now provide also a molecular basis of how phenotypically relevant missense mutations in GDF-5 might impair receptor binding and activation.

SUBMITTER: Kotzsch A

PROVIDER: S-EPMC2670865 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Transcription factors must scan genomic DNA, recognize the cognate sequence of their control element(s), and bind tightly to them. The DNA recognition process is primarily carried out by their DNA binding domains (DBD), which interact with the cognate site with high affinity and more weakly with any other DNA sequence. DBDs are generally thought to bind to their cognate DNA without changing conformation (lock-and-key). Here, we used nuclear magnetic resonance and circular dichroism to investigate the interplay between DNA recognition and DBD conformation in the engrailed homeodomain (enHD), as a model case for the homeodomain family of eukaryotic DBDs. We found that the conformational ensemble of enHD is rather flexible and becomes gradually more disordered as ionic strength decreases following a Debye-Hückel's dependence. Our analysis indicates that enHD's response to ionic strength is mediated by a built-in electrostatic spring-loaded latch that operates as a conformational transducer. We also found that, at moderate ionic strengths, enHD changes conformation upon binding to cognate DNA. This change is of larger amplitude and somewhat orthogonal to the response to ionic strength. As a consequence, very high ionic strengths (e.g., 700 mM) block the electrostatic-spring-loaded latch and binding to cognate DNA becomes lock-and-key. However, the interplay between enHD conformation and cognate DNA binding is robust across a range of ionic strengths (i.e., 45 to 300 mM) that covers the physiologically-relevant conditions. Therefore, our results demonstrate the presence of a mechanism for the conformational control of cognate DNA recognition on a eukaryotic DBD. This mechanism can function as a signal transducer that locks the DBD in place upon encountering the cognate site during active DNA scanning. The electrostatic-spring-loaded latch of enHD can also enable the fine control of DNA recognition in response to transient changes in local ionic strength induced by variate physiological processes.

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Crystal structure analysis reveals a spring-loaded latch as molecular mechanism for GDF-5-type I receptor specificity.

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