Amino Acid Requirements for Formation of the TGF-β-Latent TGF-β Binding Protein Complexes
Copyright policy )Amino Acid Requirements for Formation of the TGF-β-Latent TGF-β Binding Protein Complexes
Transforming growth factor beta (TGF-beta) is secreted primarily as a latent complex consisting of the TGF-beta homodimer, the TGF-beta propeptides (called the latency-associated protein or LAP) and the latent TGF-beta binding protein (LTBP). Mature TGF-beta remains associated with LAP by non-covalent interactions that block TGF-beta from binding to its receptor. Complex formation between LAP and LTBP is mediated by an intramolecular disulfide exchange between the third 8-cysteine (8-Cys3) domain of LTBP with a pair of cysteine residues in LAP. Only the third 8-Cys domains of LTBP-1, -3, and -4 bind LAP. From comparison of the 8-Cys3(LTBP-1) structure with that of the non-TGF-beta-binding 8-Cys6(fibrillin-1), we observed that a two-residue insertion in 8-Cys3(LTBP-1) increased the potential for disulfide exchange of the 2-6 disulfide bond. We further proposed that five negatively charged amino acid residues surrounding this bond mediate initial protein-protein association. To validate this hypothesis, we monitored binding by fluorescence resonance energy transfer (FRET) analysis and co-expression assays with TGF-beta1 LAP (LAP-1) and wild-type and mutant 8-Cys3 domains. FRET experiments demonstrated ionic interactions between LAP-1 and 8-Cys3. Mutation of the five amino acid residues revealed that efficient complex formation is most dependent on two of these residues. Although 8-Cys3(LTBP-1) binds proTGF-betas effectively, the domain from LTBP-4 does so poorly. We speculated that this difference was due to the substitution of three acidic residues by alanine, serine, and arginine in the LTBP-4 sequence. Additional experiments with 8-Cys3(LTBP-4) indicated that enhanced binding of LAP to 8-Cys3(LTBP-4) is achieved if the residues A, S, and R are changed to those in 8-Cys3(LTBP1) (D, D, and E) and the QQ dipeptide insertion of LTBP-4 is changed to the FP in 8-Cys3(LTBP-1). These studies identify surface residues that contribute to the interactions of 8-Cys3 and LAP-1 and may yield information germane to the interaction of 8-Cys domains and additional TGF-beta superfamily propeptides, an emerging paradigm for growth factor regulation.
- University of Oxford United Kingdom
- New York University United States
Models, Molecular, Binding Sites, TNF Receptor-Associated Factor 3, Macromolecular Substances, Molecular Sequence Data, Intracellular Signaling Peptides and Proteins, Cell Line, Protein Structure, Tertiary, Latent TGF-beta Binding Proteins, Mutation, Fluorescence Resonance Energy Transfer, Animals, Humans, Protein Isoforms, Amino Acid Sequence, Cysteine, Disulfides, Amino Acids, Sequence Alignment, Protein Binding
Models, Molecular, Binding Sites, TNF Receptor-Associated Factor 3, Macromolecular Substances, Molecular Sequence Data, Intracellular Signaling Peptides and Proteins, Cell Line, Protein Structure, Tertiary, Latent TGF-beta Binding Proteins, Mutation, Fluorescence Resonance Energy Transfer, Animals, Humans, Protein Isoforms, Amino Acid Sequence, Cysteine, Disulfides, Amino Acids, Sequence Alignment, Protein Binding
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