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In order to analyse whether a C-terminal polybasic sequence represents a nuclear localization signal (NLS) we obtained several truncated and mutant forms of protein of regerating liver (PRL)-3 and evaluated their subcellular localization as compared to the wild-type form. Our results invalidate the hypothesis that this is an NLS. We also analysed the influence of the C- and N-terminal residues on the phosphatase activity of PRL-3. Our results provide in vitro evidence that the C-terminal CAAX motif, besides directing the protein farnesylation, plays an additional regulatory role by inhibiting the catalytic efficiency of PRL-3. Taking into account the results we obtained, as well as reported data, we propose a hypothetical molecular mechanism for the nucleocytoplasmic localization and transfer of PRL-3.

Publisher Summary This chapter elaborates the structural chemistry and the biological aspects of hydra matrix metalloproteinase (HMMP). HMMP has a similar domain organization to that seen in vertebrate MMPs such as MMP-1 or MMP-3. Comparison of the amino acid sequence of HMMP with other MMPs shows that HMMP has an overall 30–35% identity with known MMPs. The sequence identity is about 10% higher if only the catalytic domains are compared. The sequences of two critical regions, the Cysswitch and catalytic Zn2+-binding region are well conserved in HMMP. The hinge region of HMMP is somewhat hydrophilic in nature, suggesting that this region is exposed as shown by the crystal structure of the full-length porcine MMP-1. The region of lowest identity is the C-terminal hemopexin domain. A detailed analysis of the HMMP sequence indicates that this enzyme has many similarities to vertebrate MMPs but also a number of features that make it unique. One region of variation in HMMP is the cysteine-switch region where a leucine residue is substituted for the valine residue typically seen in many vertebrate MMPs.

Publisher Summary This chapter examines the structural chemistry and the biological aspects of hydra metalloproteinase 1 (HMP1). Hydra metalloproteinase 1 is a member of the astacin class of metalloproteinases. Astacin metalloproteinases include members such as crayfish astacin and human bone morphogenetic protein 1, and meprin and tolloid proteins of different organisms. These proteinases have been associated with a broad spectrum of biological activities such as food digestion, egg shell hatching, processing of growth factors, and axis determination and cell differentiation during development in a wide variety of organisms. These diverse functions are attributed to an intrinsic proteolytic activity that is involved with direct processing of substrates, indirect modulation of growth factor activity, and assembly and integrity of the extracellular matrix. On the other hand, in addition to osteogenetic activity, BMP-1 also possesses the ability to modify the deposition and composition of basement membrane, acting as type I procollagen C-proteinase. A modified immunocytochemical procedure demonstrated that HMPl protein can be localized not only to ECM of tentacles, but also endodermal cells of the body column in a pattern similar to its mRNA distribution.