Identification of a haem-utilization protein (Hup) in Haemophilus influenzae

Haemophilus influenzae has an absolute growth requirement for a porphyrin source. This growth requirement can be satisfied in vitro by haem, haemoglobin or the haemoglobin-haptoglobin, haem-haemopexin and haem-albumin complexes. A family of proteins, termed the Hgp proteins, which are essential for utilization of the haemoglobin-haptoglobin complex, has previously been identified. A strain lacking the Hgp proteins also has a residual ability to utilize haemoglobin, indicating that additional moieties contribute to haemoglobin utilization. Using a haemoglobin affinity method an approximately 105 kDa protein was isolated. Mutation of the identified gene in an Hgp null background reduced the ability of the mutant strain to utilize haemoglobin in vitro. The mutation also resulted in a reduced ability to utilize haem, haem-haemopexin, haem-albumin and haemoglobin-haptoglobin, thus identifying a general haem-utilization protein (Hup) in Haemophilus influenzae.