The HQ (H = histidine, Q = glutamine) tag is a small fusion tag that can be isolated using immobilized metal affinity columns. HQ-tagged proteins can be expressed and purified from bacterial cells under native and denaturing conditions, mammalian cells, insect cells, wheat germ and rabbit reticulocyte. Furthermore, HQ-tagged proteins can be purified using magnetic or non-magnetic resins in multiple formats from small to large-scale and manual or automated. In this chapter, we have described various protocols for the purification of HQ-tagged proteins.
