Hirudins and hirudin-like factors in Hirudinidae: implications for function and phylogenetic relationships

Abstract

Haematophagous leeches express a broad variety of bioactive factors that are released from the salivary gland cells into the wound of a host during feeding. Among these, hirudin is probably the best studied factor and, moreover, the only one that has successfully made the transition from nature to clinical use. Many components of the leech saliva still remain either poorly characterized or yet completely unknown. Only recently, a new class of leech-derived factors has been discovered in Hirudo medicinalis, the hirudin-like factors (HLFs). HLFs comprise typical structural features of hirudin but lack others. We were able to verify the expression of HLFs not only in two additional species of the genus Hirudo, but also in Hirudinaria manillensis. Various phylogenetic analyses based on gene and protein sequences support a sister group relationship between hirudins and HLFs. Although potential molecular targets of HLFs remain unknown, the presence of multiple isoforms in individual leeches of different genera points to key functions in the regulation of several processes associated with the blood-sucking life style of leeches.

Hirudin or hirudin‐like factor ‐ that is the question: insights from the analyses of natural and synthetic HLF variants

“…However, such a definition negates the evolutionary perspective because it would include factors such as HV1 and HM1, but exclude, for example, HLF1V and Hirudin Mdec . As already mentioned above, HV1, HM1, HLF1, and Hirudin Mdec comprise an identical gene structure and hence share a common ancestor and consequently the same evolutionary origin . We do not have a solution that answers all questions and includes all possible aspects of the problem, but for now, we propose the following terminology: ‘classical hirudins’ are the hirudins in a narrow sense, for example, HV1 and HM1 ‘unorthodox hirudins’ are factors that lack the additional motifs of classical hirudins (as mentioned above), but comprise antithrombin activity, for example, HLF5, HLF8, HLF1V, and Hirudin Mdec ‘HLFs’ are factors that comprise the key structural features of hirudins, but lack the antithrombin activity, for example, HLF1 and HLF6. …”

“…And indeed, there are pronounced differences in the primary structure (amino acid sequence) of full hirudins, unorthodox hirudins, and HLFs. Common theme are the six conserved cysteine residues, but features such as the length and composition of the C‐terminal tail, the number and position of positively (hence basic) or negatively (hence acidic) charged amino acid residues, or the overall pI value (isoelectric point) differ in a wide range . Interestingly, all full and also all unorthodox hirudins that were functionally tested so far and that exhibited an anticoagulatory and antithrombin activity (justifying their classification as hirudins) comprise a pI value of about 4.1–4.6.…”

“…. Later on, the cDNAs and genes of several HLF1 variants could be identified in specimens of H. medicinalis , Hirudo verbana, and Hirudo orientalis , respectively . HLF1 is of about the same length (62 aa) as the hirudin variants (65–66 aa) and comprises a C‐terminal tail that contains a large number (13) of acidic amino acid residues.…”

Draft genome sequences ofHirudo medicinalisand salivary transcriptome of three closely related medicinal leeches

“…The functional segregation of hirudin and hirudin-like factor genes could be an example of this. The functions of hirudin are well understood, while targets of hirudin-like factors are still not known [88,89]. Moreover, the results show that many well known blood meal-related genes are found in single-copies (without duplication) including Saratin, Leech DTI and Carboxy peptidase inhibitor.…”

The Genome of Medicinal Leech (Whitmania pigra) for Exploration of Bioactive Ingredients

“…As the most well-studied natural anticoagulant from leeches, hirudin has served as a standard for designing natural coagulation inhibitors [13]. Hirudin may be useful in the therapy of thrombosis because of its specific antithrombin effects [14].…”