Azurin is a periplasmic 128
amino acid protein in Pseudomonas aeruginosa, termed Paz, which has been shown to enter preferentially and induce apoptosis in
cancer cells such as human
melanoma or
breast cancer. Its effectiveness against
brain tumors such as
glioblastomas has not been studied. The
meningitis-causing bacterium Neisseria meningitidis also harbors an
azurin-like
protein. Unlike all other known azurins, Neisserial
azurin, termed Laz, is surface-exposed and has in its N-terminal region a 39
amino acid epitope called H.8. Upstream of this H.8 moiety is a lipobox that results in the truncation of the
protein at the N-terminal
cysteine residue with modification by a
lipid group. No function of Laz is known. We demonstrate that while Paz is deficient in entering
glioblastoma cells and exhibits low cytotoxicity, Laz is much more proficient in entering
glioblastoma cells and shows a higher level of cytotoxicity. When the Neisserial H.8 moiety containing the lipobox is fused in frame with Paz either in its N-terminal (H.8-Paz) or in its C-terminal (Paz-H.8), both had high cytotoxicity for
glioblastoma cells and a higher level of internalization. When expressed in E. coli, H.8-Paz was much more exposed on the surface than Paz-H.8. The replacement of the Laz N-terminal
cysteine residue involved in acylation with an
alanine residue abolished the surface display, but had no effect on cytotoxicity or entry in
glioblastoma cells, suggesting a role of the H.8 moiety, but not its lipidation, in disrupting the entry barrier in
brain tumor cells.