This family contains the Syd protein that has been implicated in the Sec-dependent transport of polypeptides across the inner membrane in bacteria. Syd has been shown to bind the SecY subunit of membrane-embedded SecYEG heterotrimer (also known as core translocon or SecY complex) which is a conserved protein-conducting channel essential for the biogenesis of most of the secretory and integral membrane proteins. The SecY-binding site of Syd is a conserved concave and electronegative groove that forms interactions with the electropositive loops of the SecY subunit. Syd is also known to verify the proper assembly of the SecY complex in the membrane by interfering with protein translocation only when the channel displays abnormal SecY-SecE associations. Operon analysis has shown that Syd protein may function as immunity protein in bacterial toxin systems.