Catalyzes the transfer of myristate from myristoyl-acyl carrier protein (ACP) to Kdo(2)-(lauroyl)-lipid IV(A) to form Kdo(2)-lipid A. Can probably also catalyze the transfer of myristate to Kdo(2)-(palmitoleoyl)-lipid IV(A) to form the cold-adapted Kdo(2)-lipid A. dodecanoyl-(Kdo)2-lipid IVA + tetradecanoyl-[ACP] = alpha-Kdo-(2->4)-alpha-Kdo-(2->6)-lipid A + holo-[ACP] (9Z)-hexadecenoyl-(Kdo)2-lipid IVA + tetradecanoyl-[ACP] = ((9Z)-hexadecenoyl-tetradecanoyl)-(Kdo)2-lipid A + holo-[ACP] Glycolipid biosynthesis; KDO(2)-lipid A biosynthesis; KDO(2)-lipid A from CMP-3-deoxy-D-manno-octulosonate and lipid IV(A): step 4/4. Bacterial outer membrane biogenesis; lipopolysaccharide biosynthesis. Induced under limited magnesium growth conditions by the PhoP/PhoQ two-component system. A msbB1/msbB2 double mutant is impaired in its capacity to cause TNF-alpha production by human monocytes and to cause rupture and inflammatory destruction of the epithelial barrier in the rabbit ligated intestinal loop model of shigellosis. Mutants have no defect in their ability to enter into epithelial cells. Belongs to the LpxL/LpxM/LpxP family. LpxM subfamily. Extended N-terminus.