Tethering cysteine residues using cyclic disulfides

A method comprising the step of

• contacting a compound of Formula I or a compound of Formula II with a first protein and a second protein under conditions suitable for cross-linking the first protein to the second protein, thereby cross-linking the first protein to the second protein,
• wherein
• the first protein comprises a first cysteine residue;
• the second protein comprises a second cysteine residue;
• the compound of Formula I is
• wherein
• Y is S, S═O, or S(═O)2;
• n is 0, 1, 2, 3, or 4;
• and
• R is independently selected from the group consisting of —H, —OH, —NH2, —NHR′, —N(R′)2, alkyl, -OMs, -OTs, -OTf, and —CO2H;
• or any two geminal R groups, taken together, form an imine;
• or any two vicinal R groups, taken together, form a ring;
• wherein any alkyl or imine may be substituted with a carbamide, a carboxylate, or a hydroxyl;
• and
• R′ is alkyl or aryl;
• and
• the compound of Formula II is
• wherein
• R″ is —H, alkyl, or aryl, or both R″, taken together, form a ring;
• wherein any alkyl, aryl, or ring may be substituted with —OH, alkyl, or halo.