Role of basic residues of human lactoferrin in the interaction with B lymphocytes

We have previously demonstrated that lactoferrin was incorporated into a ly mphocytes and that a trypsin treatment for a short period reduced the numbe r of lactoferrin molecules incorporated into B lymphocytes, An N-terminal s equence analysis revealed that the mild trypsin treatment had cleaved the t hree N-terminal amino acids, Gly(1)-Arg(2)-Arg(3). Chemical conjugation of lost sequence analogue Gly-Arg-Arg-Gly with the mildly digested lactoferrin recovered the interaction with a lymphocytes, while conjugation of acctyl- Arg-Arg-Gly, a deamino analogue of Gly-Arg-Arg-Gly, did not recover the int eraction, This shows that the N-terminal basic region containing N-terminal Cry played an important role in the interaction with B lymphocytes. Acylat ion of the amino groups of lactoferrin also significantly reduced the inter action with a lymphocytes, and an O-methylisourea treatment of the amino gr oups, which preserved the positive charge, hardly affected the interaction. These results suggest that both the N-terminal basic region and the basic characteristics of the whole molecule contributed to its interaction with B lymphocytes.