How does SDS bind to proteins and make them negative if the molecule itself has a charge of 0?

Answer 1

SDS (Sodium Dodecyl Sulfate or [CH3-(CH2)10-CH2-O-SO-3]Na+) is a detergent under the category of amphipathic molecules (those molecules that have both polar or hydrophilic, and nonpolar or hydrophobic groups) and is a strong denaturant chemical that disrupts the terciary structure of proteins (without breaking disulfide bonds) to give a random coil or rod-like shape configuration.

SDS binds quite tenaciously to proteins (an average of one SDS molecule for every two amino acid residues). The large negative charge that SDS imparts masks the protein's intrinsic charge so that SDS-treated proteins tend to have identical charge-to-mass ratios and similar shapes, useful characteristics to determine their molecular masses through SDS-PAGE electrophoresis techniques.

Answer 2

SDS molecules contain a negatively charged sulfate group that binds to the proteins, causing them to become negatively charged when surrounded by SDS. This interaction occurs through electrostatic interactions between the positively charged amino acids in the protein and the negatively charged sulfate groups on SDS.