Purification and characterization of the lysozyme from the gut of the softtick Ornithodoros moubata

The gut of the adult soft ticks Ornithodoros moubata displays high lytic ac tivity against the bacteria Micrococcus luteus. The activity differed in th e range of two orders of magnitude among individual animals and increased o n average 4 fold during the first week following ingestion. In homogenates of first instar nymphs the activity was much lower increasing exponentially as nymphs neared the first molt. The protein responsible for this activity was purified out of gut contents of adult ticks by means of affinity adsor ption on magnetic-chitin followed by two chromatography steps on cation exc hange FPLC column MonoS. The homogeneous active protein has a mass of 14006 +/-20 Daltons as determined by MALDI-TOF mass spectrometry. The N-terminal amino-acid sequence of this protein is K-V-Y-D-R-C-S-L-A-S-E-L-R with the h ighest similarity to the lysozyme from liver of rainbow trout and to lysozy mes from digestive tracts of several mammals. The motif DRCSLA is specific for the digestive lysozymes of several dipteran insects. Based on this evid ence, we have identified the protein as the tick gut lysozyme. The tick gut lysozyme has a pi near 9.7 and retains its full activity after treatment a t 60 degrees C for 30 minutes. The pH optimum of the tick lysozyme was in t he range from pH 5-7. Only marginal activity could be detected at pH>8 whic h raises the question about the function of lysozyme in antibacterial defen se in the environment of the tick gut. (C) 1999 Elsevier Science Ltd. All r ights reserved.