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]):

• . The angle measured here reflects the shift of one monomer in the bound structure relative to the same monomer in the apo structure. .
• (b) Front orientation of the alignment. RGD indicates the integrin binding motif. (c) 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.

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