In previous studies, interactions of Hi-aeg strains were shown to be more analogous to Nm (Virji et al., 2000) . The current studies accordingly demonstrated a requirement both for Ile-91 and Tyr-34 for all Hi-aeg (Fig. 5) . In addition, as with some Nm strains, the requirement for hydrophobic and aliphatic chains was partly fulfilled by Leu and to a lesser extent by Thr. Substitutions of residue Tyr-34 with Phe or Ser produced a complex profile. Phe generally created a suitable or better environment but the loss of the aromatic ring was also tolerated (Y34S). At position 89, Q > N substitution enhanced binding dramatically for Ha3.