Crosslinking reagents disulfide containing

Thiol-modified HA is created by coupling of disulfide-containing dihydrazide reagents to the -COOH groups via carbodiimide chemistry, followed by reduction to expose the thiol groups [46,47]. The thiol-modified HA (Figure 2.1c) will spontaneously crosslink to form hydrogels [46, 47]. 

SMPT, succinimidyloxycarbonyl-a-methyl-a-(2-pyridyldithio)toluene, contains an NHS ester end and a pyridyl disulfide end similar to SPDP, but its hindered disulfide makes conjugates formed with this reagent more stable (Thorpe et al., 1987) (Chapter 5, Section 1.2). The reagent is especially useful in forming immunotoxin conjugates for in vivo administration (Chapter 21, Section 2.1). A water-soluble analog of this crosslinker containing an extended spacer arm is also commercially available as sulfo-LC-SMPT (Thermo Fisher). 

Figure 6.2 The trifunctional reagent sulfo-SBED reacts with amine-containing bait proteins via its NHS ester side chain. Subsequent interaction with a protein sample and exposure to UV light can cause crosslink formation with a second interacting protein. The biotin portion provides purification or labeling capability using avidin or streptavidin reagents. The disulfide bond on the NHS ester arm provides cleavability using disulfide reductants, which effectively transfers the biotin label to an unknown interacting protein.

The most common type of heterobifunctional reagent used for the activation of lipid components includes the amine- and sulfhydryl-reactive crosslinkers containing an N-hydroxysuccinim-ide (NHS) ester group on one end and either a maleimide, iodoacetyl, or pyridyl disulfide group on the other end (Chapter 5, Section 1). Principle reagents used to effect this activation process include SMCC (Chapter 5, Section 1.3), MBS (Chapter 5, Section 1.4), SMPB (Chapter 5, Section 1.6), SIAB (Chapter 5, Section 1.5), and SPDP (Chapter 5, Section 1.1). Other... 

Iodoacetate derivatives have been used for decades to block or crosslink sulfhydryl groups in proteins and other molecules (Chapter 1, Section 5.2). At mildly alkaline pH values (pH 8-8.5), iodoacetyl derivatives are almost entirely selective toward the cysteine —SH groups in proteins. Disulfide reduction or thiolation reagents can be used to create the required sulfhydryl groups on proteins containing no free sulfhydryls. 

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