A search within the IL-1 type I receptor reveals a peptide with hydropathic complementarity to the IL-1 beta trigger loop which binds to IL-1 and inhibits in vitro responses

In previous research, we were able to demonstrate that a seven amino acid r esidue peptide (VITFFSL), designed as an antisense peptide of the P-bulge t rigger loop region of interleukin 1 beta (IL-1 beta) (QGEESND, residues 48- 54 [mature protein sequence]), was able to interact with IL-1 specifically and inhibit the response to IL-1 in an in vitro bioassay. The evidence was consistent with a specific interaction ocurring between antisense peptide a nd the trigger loop region. On the basis that antisense peptides are able t o interact with their corresponding sense peptide sequences as a result of their mutually complementary hydropathic profiles (Fassina G., Verdoliva, A ., Cassani, G., Melli, M., 1994. Binding of type I IL-1 receptor fragment 1 51-162 to IL-1. Growth Factors 10, 99-106; Maier, C.C,, Moseley, H.N.B., Zh ou, S., Whitaker, J.N., Blalock, J.E., 1994. Indentification of interactive determinants on idiotypic-anti-idiotypic antibodies through comparison of their hydropathic profiles. Immunomethods 5, 107-113), we devised a compute r program (FINDH) to search the amino acid residue sequence of interleukin- 1 type 1 receptor (IL-1 R1) for peptide motifs possessing hydropathic compl ementarity to the trigger loop sequence. The most complementary "best-fit p eptide" motif (LITVLNI) was located in the third extracellular domain of IL -I R1. A best-fit peptide corresponding to this motif was synthesised and f ound to bind to IL-1 beta as well as inhibit the response to IL-1 in two in dependent in vitro bioassays (monitoring IL-1 dependent serum amyloid A syn thesis and IL-1 dependent alkaline phosphatase activity, respectively), A s econd peptide motif (VIEFITL) was identified and the corresponding peptide synthesised along with a reordered version (LTILINV) of the best fit peptid e, Both failed to bind measurably with IL-1 beta or inhibit the response to IL-1 in the two bioassays. This best fit peptide behaved very similarly, i n terms of IL-1 binding and inhibition behaviour, to the original trigger l oop antisense peptide, Reference to the recently released X-ray crystal str ucture of IL-1 and the IL1-R1 extracellular domain shows that the best fit peptide motif in IL-1 R1 is not apparantly interacting with the IL-1 beta t rigger loop, although both are close in space, The intriguing possibility e xists that the best fit peptide motif could represent an alternative site f or IL-1 beta receptor interaction which has not thus far been identified. ( C) 2000 Elsevier Science Ltd. All rights reserved.