SARS Coronavirus Fusion Peptide-Derived Sequence Suppresses Collagen-Induced Arthritis in DBA/1J Mice

Shen, Zu T.; Sigalov, Alexander B.

As mentioned above, the 19 amino acid-long hydrophobic stretch corresponding to residues 770 to 788 (MYKTPTLKYFGGFNFSQIL) has been recently identified as the putative fusion peptide of the SARS-CoV S2 subunit 10 . In the present study, in order to provide compelling experimental in vivo evidence to support our hypothesis 29 , we used the SCHOOL model to design a 11-mer synthetic peptide MG11 (MYKTPTLKYFG) derived from the SARS-CoV FP sequence with the positioning of two essential positively charged lysine residues (underlined) spaced by four amino acids. The model suggests that this charge distribution pattern is functionally important to provide TCR-targeted inhibitory activity 13, 29, 42, 44 . If our hypothesis is correct, the MG11 peptide should demonstrate the immunomodulatory activity in vivo similar to that demonstrated earlier for TCR CP and HIV gp41 FP in animal models of autoimmune arthritis 18, 20, 21, 23 . The SARS CoV FP peptide mutant with lysines replaced by glycines (MG11-2G) was used as a negative control peptide. According to the SCHOOL model 13, 29 , this peptide cannot compete with the recognition TCRα subunit for binding to ζ ζ and CD3ε δ signaling homoand heterodimers (Fig. 1) , and thus cannot inhibit TCR signaling. Because of discrepancies found in prior studies of the immunomodulatory activity of TCR inhibitory TM peptides between in vitro (no activity observed) and in vivo (anti-arthritic activity observed in rats with adjuvant-induced arthritis, AIA) data 23 , in this study, we moved directly to in vivo studies and tested the MG11 and MG11-2G peptides in the CIA model of autoimmune arthritis. The circulatory half-life of peptides in vivo is very short, typically only a few minutes 35 . In order to prolong the half-life of MG11, we tested in the present study whether this peptide can be incorporated into sHDL nanoparticles that mimic human HDL, a group of native lipoproteins that transport cholesterol from the peripheral tissues to the liver and can be readily reconstituted in vitro from lipids and apolipoproteins (apos) 54 . Due to the half-life of native sHDL in normal subjects being 3-5 days 36 , these particles represent a promising and versatile delivery platform for peptide therapeutics. Synthetic (reconstituted) HDL have several competitive advantages as compared with other delivery platforms: 1) apo A-I, the major HDL protein, is an endogenous protein and does not trigger immunoreactions, 2) the small size (8-12 nm) allows HDL to enter and accumulate in tissue and organ areas of interest, and 3) a variety of drugs and imaging agents can be incorporated into this platform 33, 55, 56 . With respect to therapeutics, human apo A-I is a large protein, which is purified from human plasma. Thus, in addition to the immense monetary cost in purification, further development of apo A-I-containing therapeutic agents would require a number of safety precautions followed by a complicated transition into clinical practice. Previously, we demonstrated that synthetic apo A-I peptides can functionally replace the native apo A-I protein in HDL. This encourages the further development of the HDL-based delivery platform. In the present study, synthetic sHDL that contain apo A-I peptides were successfully loaded with MG11 and subsequently purified and characterized using a variety of biophysical procedures. This is the first study to test previously predicted immunomodulatory activity of SARS-CoV FP 29 . As expected from the