Journal:IUCrJ:S205225251901707X

Structural insights into conformational switching in latency-associated peptide between TGFβ-1 bound and unbound states

Timothy R. Stachowski, Mary E. Snell, and Edward H. Snell ^[1]

Molecular Tour
In response to environmental changes, proteins are released from cells that act as messengers, which allows cells to communicate with one another and coordinate a physiologic response. Transforming growth factor β-1 (TGFβ-1) is a protein used to communicate information about when and how cells should proliferate and is particularly important in organizing embryonic tissue development. The fundamental way our cells regulate TGFβ-1 activity is with a second protein, latency-associated peptide (LAP). LAP forms a complex with TGFβ-1, tethering it to the outside surface of the cell. Several pathologies including cancer progression and immune suppression are driven by an overabundance of TGFβ-1.

Because LAP binding reduces TGFβ-1 activity, recombinant LAP is a promising novel therapeutic approach, however a detailed understanding of how LAP binds TGFβ-1 is missing, which could reveal ways to improve the LAP-TGFβ-1 interaction or develop other anti-TGFβ-1 therapies. In a paper in IUCrJ, Stachowski et al. show that LAP adopts structurally distinct conformations between unbound and TGFβ-1 bound states. This was revealed by comparing the X-ray crystal structure of LAP in the unbound state (6p7j) solved by Stachowski et al. with the crystal structure of LAP bound to TGFβ-1 (3rjr) previously reported by Shi et al. 2011 ^[2]. This analysis combined with solution modelling showed that LAP transitions from an extended to compact conformation when binding TGFβ-1, simulating a type of hugging motion where LAP embraces TGFβ-1. Surprisingly, this conformational change includes rearranging two domains that are distant from one another and might be coordinated through the formation of an α-helix that is distant from the LAP-TGFβ-1 interaction site. Together, these results provide new spatial details about the TGFβ-1 binding mechanism, specifically how LAP reorients itself to develop the LAP-TGFβ-1 interface. This insight is important as it provides new avenues to engineer and improve LAP as a therapeutic that are focused beyond just the interaction site.

Comparison of apo LAP and TGFβ-1 (LTGFβ-1) bound structures. Only residues modelled in the apo structure were included for comparison. The apo structure reported here (royalblue; PDB entry 6p7j) is aligned with pig TGFβ-1 bound LAP (yellow; PDB entry 3rjr, Shi et al., 2011^[2]):

• Side view shows the inter-monomer angle in the apo structure is 15˚ greater than in the bound structure. The angle measured here reflects the shift of one monomer in the bound structure relative to the same monomer in the apo structure. Click here to see morph.
• Front orientation of the alignment. RGD indicates the integrin binding motif. Click here to see morph.
• A close-up view of the RGD containing loop shows that it is similarly positioned in both structures, on the solvent exposed shoulder of the arm domain. For clarity, the Cα atoms of G and D (which are modelled in both structures) from the motif are shown as spheres. Click here to see morph.

PDB reference: latency-associated peptide, 6p7j.

References

1. ↑ Stachowski TR, Snell ME, Snell EH. Structural insights into conformational switching in latency-associated peptide between transforming growth factor beta-1 bound and unbound states. IUCrJ. 2020 Feb 6;7(Pt 2):238-252. doi: 10.1107/S205225251901707X. eCollection, 2020 Mar 1. PMID:32148852 doi:http://dx.doi.org/10.1107/S205225251901707X
2. ↑ ^{2.0 2.1} Shi M, Zhu J, Wang R, Chen X, Mi L, Walz T, Springer TA. Latent TGF-beta structure and activation. Nature. 2011 Jun 15;474(7351):343-9. doi: 10.1038/nature10152. PMID:21677751 doi:http://dx.doi.org/10.1038/nature10152