TECHNOLOGY FOCUS - BIOTECHNOLOGY - Preparation: No preparation method is given. Preferred Components: The entity is a modified prokaryotic or eukaryotic cell, preferably a modified Escherichia coli cell, or a modified Saccharomyces cerevisiae cell. The heterologous light-powered proton pumps comprises retinal. The heterologous light-powered proton pump is proteorhodopsin or xanthorhodopsin. The molecular machine is flagellar motor, rotary ATP synthase, secretory system, ion or metabolite anti-porter or symporter, or multidrug transporter. The heterologous proton pumps provide at least 20% of the total cellular proton motive force. In the entity at least one gene encoding the heterologous light powered proton pump has been modified to reduce the rate of translation of the encoded heterologous light-powered proton pump relative to an unmodified version of the gene, where the proportion of properly folded, membrane-inserted light-powered proton pumps to improperly folded proton pumps in the entity is increased relative to the proportion comprised by an otherwise identical entity expressing an unmodified version of the gene. The heterologous proton pump is proteorhodopsin, where the immediate carboxy-terminal region of the native proteorhodopsin sequence has been deleted. The entity comprises a non-native stacked membrane structure, where the membrane structure comprises the heterologous light-powered proton pump. The modified cell is a modified Saccharomyces cerevisiae cell. The entity contains light-powered proton pumps in at least two membranes, including the plasma membrane, the inner mitochondrial membrane, or a synthetic organelle. In the system the at least one cellular compartment is vacuole, endoplasmic reticulum, golgi apparatus or plasma membrane. Preferred Method: In method (M5) the membrane structure comprises the heterologous light-powered proton pump, where the heterologous light-powered proton pump comprises a proteorhodopsin polypeptide fused to a non-proteorhodopsin polypeptide that promotes protein dimerization or oligomerization. The non-proteorhodopsin polypeptide comprises a non monomeric fluorescent protein tag, preferably a non monomeric green fluorescent protein tag. EXAMPLE - SAR86 gamma -proteobacterial PR-variant in Escherichia coli cells (RP437 DE3) was expressed using a T7 based expression system (pET200, kanamycin resistance). Then the cells were grown in tryptone broth (comprising tryptone (1%) and sodium chloride (0.5%)) supplemented with kanamycin (25 mu g/ml). Then in mid-log phase, PR expression was induced with isopropyl-beta-D-thiogalactopyranoside (1 mM) and the medium was supplemented with ethanolic all-trans-retinal (10 mu M). Cells were then collected in late log phase by centrifugation (4500g for 5 minutes) and carefully resuspended in motility medium (containing phosphate buffered saline (1 mM) and ethylenediaminetetraacetic acid (0.1 mM) at pH 7.4) to obtain the light harvesting entity.