The leukocyte ␤ 2 integrins are heterodimeric adhesion receptors required for a functional immune system. Many leukocyte adhesion deficiency-1 (LAD-1) mutations disrupt the expression and function of ␤ 2 integrins. Herein, we further characterized the LAD-1 mutation N329S in the ␤ 2 inserted (I)-like domain. This mutation converted ␣ L ␤ 2 from a resting into a high affinity conformer because ␣ L ␤ 2 N329S transfectants adhered avidly to ligand intercellular adhesion molecule (ICAM)-3 in the absence of additional activating agent. An extended open conformation is adopted by ␣ L ␤ 2 N329S because of its reactivity with the ␤ 2 activation reporter monoclonal antibodies MEM148 and KIM127. A corresponding mutation in ␤ 3 generated constitutively active ␣ IIb ␤ 3 that adhered to fibrinogen. This Asn is conserved in all human ␤ subunits, and it resides before the last helix of the I-like domain, which is known to be important in activation signal propagation. By mutagenesis studies and review of existing integrin structures, we conjectured that this conserved Asn may have a primary role in shaping the I-like domain by stabilizing the conformation of the ␣7 helix and the ␤6-␣7 loop in the I-like domain.The integrins are type I membrane cell adhesion molecules formed non-covalently by two subunits (␣/␤). Despite having no intrinsic enzymatic properties, integrins are bidirectional signal transducers brought about by the recruitment of cytosolic proteins, many of which are signaling proteins, to their relatively short cytoplasmic tails (1). Structural data reveal a composite of distinct domains and folds found in an integrin molecule (2, 3). Out of the 24 human integrins, nine contain in the ␣ subunit an additional inserted (I) domain that is the primary ligand-binding domain of these integrins (1). The I domain has a metal ion-dependent adhesion site (MIDAS) 3 that contains a divalent cation essential for ligand binding. Integrins that lack the I domain (henceforth referred to as I-less integrins) are found to bind ligand via the ␤ propeller of their ␣ subunit and the I-like domain of their ␤ subunit (2, 3). The I-like domain is found in all integrin ␤ subunits, and it is structurally similar to that of the I domain. However, it contains a specificity-determining loop, which was reported to contribute toward ligand binding specificity and integrin ␣␤ subunit association (4), and it has two additional divalent cation-binding sites. The MIDAS of the I-like domain is flanked by the adjacent to MIDAS (ADMIDAS) and the ligand-induced metal-binding site (LIMBS), which serve as negative and positive regulatory sites, respectively (5-7). The conserved coordinating residues that are involved in the three cation-binding sites of the I-like domain are highlighted (Fig. 1A).The leukocyte-restricted ␤ 2 integrins contain four members that differ in their ␣ subunits, the ␣ L ␤ 2 , ␣ M ␤ 2 , ␣ X ␤ 2 , and ␣ D ␤ 2 (1). These integrins maintain a functional immune system by their direct involvement in processes such as leukocyte adhe...

This study investigated the adsorption kinetics of dissolved copper(II) and zinc(II) by aerobic granular sludge. Two series of batch experiments were conducted at different initial copper(II), zinc(II) concentrations (Co) and initial granule concentrations (Xo). Results showed that the biosorption kinetics of individual copper(II) and zinc(II) by aerobic granules were closely related to Co and Xo. The maximum biosorption capacity of individual copper(II) and zinc(II) by aerobic granules was 246.1 mg g(-1) and 180 mg g(-1), respectively. In order to theoretically interpret the results obtained, two kinetic models previously developed for biosorption were employed and compared in this study. It was found that the model proposed by Liu et al. (2003) could fit the experimental data very well, but the second-order model failed to fit the data in some cases. It appears that aerobic granules would be potential biosorbent with high efficiency for the removal of dissolved copper(II) and zinc(II) from wastewater.