Contribution of bovine lactoferrin inter-lobe region to iron binding stability and antimicrobial activity against Staphylococcus aureus

The investigation of the recombinant bovine lactoferrin-derived antimicrobial protein (rBLfA) demonstrates that the inter-lobe region of bovine lactoferrin contributes to iron binding stability and antimicrobial activity against Staphylococcus aureus. rBLfA containing N-lobe (amino acid residues 1-333) and inter-lobe region (residues 334-344) was expressed in Pichia pastoris at shaking flask and fermentor level. The recombinant intact bovine lactoferrin (rBLf) and N-lobe (rBLfN) were expressed in the same system as control. The physical-chemical parameters of rBLfA, rBLfN and rBLf including amino acid residues, molecular weight, isoelectric point, net positive charge and instability index were computed and compared. The simulated tertiary structure and the calculated surface net charge showed that rBLfA maintained original structure and exhibited a higher cationic feature than rBLf and rBLfN. The three proteins showed different iron binding stability and antimicrobial activity. rBLfA released iron in the pH range of 7.0-3.5, whereas rBLfN lost its iron over the pH range of 7.0-4.0 and iron release from rBLf occurred in the pH range of 5.5-3.0. However, the minimum inhibition concentration of rBLfA against S. aureus ATCC25923 was 6.5 micromol/L, compared with 12.5 and 25 micromol/L that of rBLfN and rBLf, respectively. These results revealed that S. aureus was more sensitive to rBLfA than rBLfN and rBLf. It appeared that the strong cationic character of inter-lobe region related positively to the higher anti-S. aureus activity.