Conjugation reagents and methods using 1,2-cyclohexanediones
The present invention relates to methods to use cyclohexan-1,2-dione (CHD) groups to attach labels, linkers, and other molecules to a target compound comprising a CHD-reactive group such as a guanidine, amidine, urea, thiourea and the like. Methods of the invention include milder conditions than those previously known for promoting reaction of CHD with CHD-reactive groups, which makes the methods suitable for use with base-sensitive compounds and complex biomolecules. Methods of the invention are especially useful for attaching linking and labeling groups to a peptide that comprises at least one arginine residue, and can also be used to link such peptides to other target molecules such as nucleic acids. The invention also provides CHD-containing conjugation reagents and compositions comprising CHD-containing intermediates, and precursors useful for making CHD-containing compounds that can be used in the methods of the invention.
1. A method of attaching a conjugation reagent to a target molecule, wherein:
the conjugation reagent comprises a 1,2-cyclohexanedione (CHD) group; and
the target molecule comprises a CHD-reactive group;
wherein the method comprises contacting the conjugation reagent with the target molecule under reaction conditions that cause the CHD-reactive group to react irreversibly with the CHD group to form a modified target molecule having a covalent linkage connecting the conjugation reagent and the target molecule,
wherein the reaction conditions comprise an aqueous buffered medium having a pH between 7 and 11.2 and a temperature between 37° C. and 90° C. and the medium comprises a buffer having at least 0.1 M ionic strength.
2. The method of claim 1 , wherein the CHD-reactive group is a guanidine group of an arginine amino acid residue.
3. The method of claim 1 , wherein the conjugation reagent comprises at least one additional reactive handle that is stable under the reaction conditions that cause the CHD-reactive group to react irreversibly with the CHD group.
4. The method of claim 1 , wherein the covalent linkage connecting the conjugation reagent and the target molecule comprises the following substructure (A):
or a tautomer thereof, wherein:
the dashed bond to L connects the substructure (A) to the conjugation reagent;
the dashed bond to T connects the substructure (A) to the target molecule;
R 4 is an optional substituent on the cyclopentyl ring, and each R 4 is independently selected from C 1-2 alkyl, C 1-2 alkoxy, C 1-2 haloalkyl, —COOR, SO 3 R, halo, hydroxy, and CONR 2 ;
each R is independently H or C 1-4 alkyl optionally substituted with 1-3 groups selected from halo, OH, and C 1-2 alkoxy; and
n is 0, 1, 2 or 3.
5. The method of claim 1 , wherein the reaction conditions comprise an aqueous medium that includes up to 25% of an organic co-solvent.
6. The method of claim 1 , wherein at least 25% of the target molecules present react to form the modified target molecule.
7. The method of claim 3 , wherein the method further comprises contacting the additional reactive handle on the conjugation reagent of the modified target molecule with a second target molecule having a reactive handle complementary to the additional reactive handle to form a covalent linkage between the additional reactive handle and the second target molecule, thereby forming a target molecule—conjugation reagent—second target molecule conjugate.
8. A method of attaching a peptide comprising at least one arginine residue to a polynucleotide, the method comprising the steps of:
(a) contacting the peptide with a conjugation reagent comprising a first reactive handle and a 1,2-cyclohexanedione (CHD) group under reaction conditions that allows the least one arginine residue to react irreversibly with the CHD group, wherein the reaction conditions comprise an aqueous buffered medium having a pH between 7 and 11.2 and a temperature between 37° C. and 90° C. and the medium comprises a buffer having at least 0.1 M ionic strength, and the first reactive handle is attached or is configured to be attached to the polynucleotide or to a second reactive handle attached to the polynucleotide;
(b) optionally, attaching the first reactive handle to the polynucleotide or to the second reactive handle attached to the polynucleotide.
9. The method of claim 8 , further comprising the following steps: (i) before contacting the peptide with the conjugation reagent, contacting the peptide with a site-specific protease that is configured to cleave the peptide at arginine residue(s), thereby producing at least one fragmented peptide having a single arginine residue at its carboxyl terminus; and (ii) immobilizing the at least one fragmented peptide to a solid support via a linker, wherein the at least one fragmented peptide is contacted with the conjugation reagent.
10. The method of claim 9 , wherein immobilizing comprises covalently attaching the peptide to the solid support via a cleavable linker.
11. The method of claim 9 , wherein the step (ii) is performed before the step (a).
12. A method of analyzing a peptide comprising at least one arginine residue, the method comprising the steps of:
(a) providing a conjugate of the peptide and a recording tag, the conjugate attached to a solid support, wherein the recording tag comprises a polynucleotide that is conjugated to the peptide according to the following steps:
(i) contacting the peptide with a conjugation reagent comprising a first reactive handle and a 1,2-cyclohexanedione (CHD) group under reaction conditions that allows the least one arginine residue to react irreversibly with the CHD group, wherein the reaction conditions comprise an aqueous buffered medium having a pH between 7 and 11.2 and a temperature between 37° C. and 90° C. and the medium comprises a buffer having at least 0.1 M ionic strength, and the first reactive handle is attached or is configured to be attached to the polynucleotide or to a second reactive handle attached to the polynucleotide; and
(ii) optionally, attaching the first reactive handle to the polynucleotide or to the second reactive handle attached to the polynucleotide;
(b) contacting the peptide of the conjugate with a binding agent capable of binding to the peptide, wherein the binding agent comprises a coding tag that comprises identifying information regarding the binding agent;
(c) transferring the identifying information from the coding tag to the recording tag to generate an extended recording tag; and
(d) analyzing the extended recording tag, thereby analyzing the peptide.
13. The method of claim 12 , wherein analyzing the peptide comprises identifying at least one component of the peptide.
14. The method of claim 1 , wherein the aqueous medium has a pH between 7 and 10.
15. The method of claim 1 , wherein the buffer has an ionic strength of at least 0.5 M.
16. The method of claim 1 , wherein the reaction conditions comprise temperature between 60° C. and 90° C.
17. The method of claim 8 , wherein the aqueous medium has a pH between 7 and 10.
18. The method of claim 9 wherein the buffer has an ionic strength of at least 0.5 M.
19. The method of claim 12 , wherein the aqueous medium has a pH between 7 and 10.
20. The method of claim 19 , wherein the reaction conditions comprise temperature between 60° C. and 90° C., and the aqueous medium comprises a buffer having at least 0.5 M ionic strength.