Involved in the uptake of chitosugars. In the absence of chitobiose, expression of chiPQ is silenced by the MicM small regulatory RNA (sRNA), which sequesters the ribosome binding site of the chiPQ mRNA by an antisense mechanism. In the presence of chitosugars, the chbBCARFG chitobiose operon is induced and acts as an RNA trap to degrade the constitutively expressed MicM, leading to the translation of chiPQ. Belongs to the outer membrane porin (Opr) (TC 1.B.25) family.