Sp1 polypeptides, modified sp1 polypeptides and uses thereof
a technology of sp1 and polypeptide, which is applied in the direction of peptide sources, peptide/protein ingredients, drug compositions, etc., can solve the problems of insufficient soluble sp1 in aqueous solution, adverse side effects in therapeutic concentration, and many drugs employed to treat diseases, etc., to achieve the effect of enhancing the solubility of a substance and enhancing the solubility of the substance in the solution
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example 1
Structure of the SP1 Protein
[0257]SDS gel electrophoresis analysis of both native SP1 and its recombinant form shows that SP1 appears in two forms: a monomer (12.4-kDa) which appears when the sample is boiled in the gel application buffer in the presence of SDS and in an oligometric form (116-kDa protein) which appear when SP1 is not boiled prior to application on PAGE (see Wang et al 2002, Dgany 2004, Wang et al 2006, U.S. patent application Ser. No. 10 / 443,209). Several methods have been employed to demonstrate that SP1 in solution forms a dodecamer with a molecular weight of 150 kDa. Equilibrium analytical ultracentrifugation was employed to analyze the SP1 oligomeric state. As SP1 concentration approached zero, the measured molecular mass of the SP1 particles in solution (144 kDa at 5.6 μM monomer concentration) approached the value calculated for a dodecamer (148 kDa).
[0258]SP1 was subjected to MALDI-TOF-MS. The data revealed 12 protein peaks, of which the first (12338 Da) was ...
example 2
SP1 is a Boiling- and Denaturing-Stable, and Protease-Resistant Molecule
[0268]The stability of the SP1 complex in the presence of SDS was examined by incubating purified SP1 with SDS at different molar ratios and at different temperatures. Dissociation of the SP1 complex to monomers required a molar ratio greater than 600:1 (SDS:SP1-monomer) accompanied by boiling before loading onto the gel. Without boiling, even at a ratio of 3467 to 1, SP1 remained as a complex on SDS-PAGE. Incubation of SP1 with 1734-fold SDS (1%) at temperatures of 80° C. or lower did not cause significant disassociation of the complex (Wang 2006).
[0269]SP1 protein exhibits exceptional heat stability, which allows partial extraction of crude cellular preparations by heat treatment, as mentioned in Example 1 hereinabove. FIG. 6 shows the degree of purity achieved by heat treatment.
[0270]Differential scanning calorimetry study of SP1 indicates in a Tm of 107° C. for SP1. These results further support our previous...
example 3
SP1 Variants
[0274]SP1 variants can be constructed to enhance, or otherwise alter SP1 stability, capabilities for oligomerization and / or binding and / or complexing with other molecules and / or ability to form inter-subunit disulfide bonds and / or change the dimension of the central cavity. Numerous SP1 variant proteins were constructed to investigate the effects of specific alterations on properties of SP1.
[0275]The N-terminal segment points toward the solvent and apparently is not involved in protein folding or stability. Therefore it was predicted that N-terminus mutations would not alter protein structure or its stability. In agreement with this prediction all the N-terminus mutants including a mutant protein carrying deletion of the entire N-terminus Δ2-6 assembled into a stable complex (FIG. 3). Further, it was surprisingly uncovered that when the tumor recognition peptides CRGD (SEQ ID NO:5) and RGDC (SEQ ID NO:6) and RGD loop (SEQ ID NO:10) were inserted into the SP1 N-terminus, ...
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