Part of the type VI secretion system specialized secretion system, which delivers several virulence factors in both prokaryotic and eukaryotic cells during infection (PubMed:21555399). Forms the spike at the tip of the elongating tube formed by haemolysin co-regulated protein Hcp. Allows the delivery of the VasX antibacterial toxin to target cells where it exerts its toxicity (PubMed:21555399). Mutants are unable to secrete VasX. Belongs to the VgrG protein family.