Effector involved in the disease saprolegniosis in salmonids and other freshwater fish, resulting in considerable economic losses in aquaculture (Probable). Within the host fish cells, Htp1 is involved in the uptake of the S.parasitica effector Htp3 at a neutral pH (pH 7.5) and its release from vesicles into host cytosol where it degrades nucleic acids (PubMed:29904064). Interacts with the effector Htp3 within the host cells. Host cell surface binding and uptake is mediated by an interaction with tyrosine-O-sulfate-modified cell surface molecules and not via phospholipids, as has been reported for RxLR-effectors from plant pathogenic oomycetes. Highly expressed in zoospores/cysts from S.parasitica and in the very early stages of infection on Oncorhynchus mykiss (rainbow trout) cells. Has a conserved RxLR motif that acts to carry the protein into the host cell cytoplasm. Lacks the 'so-called' EER motif, which is found closely behind the RxLR motif in most of RxLR effector family members, but the presence of an EER motif is not always essential for the translocation of every RxLR effector into host cells, or for inducing a hypersensitive response. Belongs to the RxLR effector family.