Labeled polypeptide, modified polypeptide, production method for these polypeptides, reagent containing these polypeptides, and measurement method for target substance

A production method for a modified polypeptide, the method comprising:

• contacting, in the presence of a transglutaminase, a glutamine residue-containing polypeptide with a linker represented by formula (VI) below:
• NH2—X—Y—SH (VI)
• (wherein X represents a straight chain alkylene group, Y represents a polyethylene glycol chain, the polyethylene glycol chain having a molecular weight of 1100 or larger), to bind the linker to a carboxamide side chain of the glutamine residue;
• and
• obtaining a modified polypeptide produced by binding the carboxamide side chain with the linker;
• and,
• in the modified polypeptide,
• a side chain of the glutamine residue is represented by formula (II) below:
• (wherein, (C) represents an α-carbon atom of the glutamine residue, X represents a straight chain alkylene group, Y represents a polyethylene glycol chain, and the polyethylene glycol chain has a molecular weight of 1100 or larger).

A production method for a labeled polypeptide, the method comprising:

• contacting, in the presence of a transglutaminase, a glutamine residue-containing polypeptide with a linker represented by formula (VI) below:
• NH2—X—Y—SH (VI)
• (wherein X represents a straight chain alkylene group, Y represents a polyethylene glycol chain, the polyethylene glycol chain having a molecular weight of 1100 or larger), to bind the linker to a carboxamide side chain of the glutamine residue;
• obtaining a modified polypeptide produced by binding the carboxamide side chain with the linker;
• contacting the modified polypeptide with a maleimide group-containing label, to bind the label to the linker bound to the modified polypeptide;
• and
• obtaining a labeled polypeptide produced by binding the modified polypeptide and the label,
• and,
• in the labeled polypeptide,
• a side chain of the glutamine residue is represented by formula (I) below:
• (wherein, (C) represents an α-carbon atom of the glutamine residue, X represents a straight chain alkylene group, Y represents a polyethylene glycol chain, Z represents a label, L represents a spacer or an atomic bond, and the polyethylene glycol chain has a molecular weight of 1100 or larger).