PubMed · 8236448
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S R Sprang. 1993. On a (beta-) roll.. https://doi.org/10.1016/0968-0004(93)90061-q
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Marine picocyanobacteria of the genera Prochlorococcus and Synechococcus, the two most abundant phototrophs on Earth, thrive in oligotrophic oceanic regions. While it is well known that specific lineages are exquisitely adapted to prevailing in situ light and temperature regimes, much less is known of the molecular machinery required to facilitate occupancy of these low-nutrient environments. Here, we describe a hitherto unknown alkaline phosphatase, Psip1, that has a substantially higher affinity for phosphomonoesters than other well-known phosphatases like PhoA, PhoX, or PhoD and is restricted to clade III Synechococcus and a subset of high light I-adapted Prochlorococcus strains, suggesting niche specificity. We demonstrate that Psip1 has undergone convergent evolution with PhoX, requiring both iron and calcium for activity and likely possessing identical key residues around the active site, despite generally very low sequence homology. Interrogation of metagenomes and transcriptomes from TARA oceans and an Atlantic Meridional transect shows that psip1 is abundant and highly expressed in picocyanobacterial populations from the Mediterranean Sea and north Atlantic gyre, regions well recognized to be phosphorus (P)-deplete. Together, this identifies psip1 as an important oligotrophy-specific gene for P recycling in these organisms. Furthermore, psip1 is not restricted to picocyanobacteria and is abundant and highly transcribed in some α-proteobacteria and eukaryotic algae, suggesting that such a high-affinity phosphatase is important across the microbial taxonomic world to occupy low-P environments.
Extracellular matrix regulation of intestinal epithelial differentiation may affect development, differentiation during migration to villus tips, healing, inflammatory bowel disease, and malignant transformation. Cell culture studies of intestinal epithelial biology may also depend on the matrix substrate used. We evaluated matrix effects on differentiation and proliferation in human intestinal Caco-2 epithelial cells, a model for intestinal epithelial differentiation. Proliferation, brush border enzyme specific activity, and spreading were compared in cells cultured on tissue culture plastic with interstitial collagen I and the basement membrane constituents collagen IV and laminin. Each matrix significantly increased alkaline phosphatase, dipeptidyl peptidase, lactase, sucrase-isomaltase, and cell spreading in comparison to plastic. However, the basement membrane proteins collagen IV and laminin further promoted all four brush border enzymes but inhibited spreading compared to collagen I. Proliferation was most rapid on type I collagen and slowest on laminin and tissue culture plastic. Basement membrane matrix proteins may promote intestinal epithelial differentiation and inhibit proliferation compared with interstitial collagen I.
Acid-induced and guanidine hydrochloride (GdnCl)-induced reversible unfolding of Escherichia coli alkaline phosphatase (AP) was characterized under equilibrium conditions. The protein was exposed to extreme conditions of pH 2.0 or 6 M GdnCl and was subsequently returned to normal conditions. Associated changes in the protein structure was probed by various spectroscopic methods. The changes in the functional properties were monitored by measuring enzymatic activity, capacity to renature spontaneously upon removal of the denaturant, and renaturation in presence of various site-specific and nonspecific effector molecules, in the absence and presence of beta-mercaptoethanol. Analysis of the fluorescence and CD spectra showed that the unfolding of the organized structures was much more extensive in 6 M GdnCl than at pH 2.0. Intrachain S-S bonds in each unfolded state were accessible to reduction by beta-mercaptoethanol. The effectors Zn2+ and ATP induced renaturation of active site only under reducing conditions, whereas Triton X-100 or alpha-crystallin needed the presence of some organized structure. The reconstituted protein from each denatured state without or with an effector showed different CD spectra. It is concluded that the active site domain of AP could be reconstituted independently of other structural domains in different pathways.