Ftesson abip2

Add abip2 description and molecular mechanism

content/3.defense-systems/abip2.md

@@ -35,6 +35,10 @@ However, with the discovery of dozens of new systems, it was categorize as one o
 
 Those systems are characterized by the presence of a reverse transcriptase domain of the "Unknown Group RT".
 
+## Molecular mechanism
+
+To our knowledge, the molecular mechanism is unknown. Similarly, for the other systems of this family, the molecular mechanism remain unknown.
+
 ## Example of genomic structure
 
 The AbiP2 is composed of 1 protein: AbiP2.